diff --git a/test/api/v3/integration/challenges/POST-challenge_flag.test.js b/test/api/v3/integration/challenges/POST-challenge_flag.test.js
new file mode 100644
index 0000000000..0f5f353b6c
--- /dev/null
+++ b/test/api/v3/integration/challenges/POST-challenge_flag.test.js
@@ -0,0 +1,62 @@
+import { v4 as generateUUID } from 'uuid';
+import {
+  generateChallenge,
+  createAndPopulateGroup,
+  translate as t,
+} from '../../../../helpers/api-integration/v3';
+
+describe('POST /challenges/:challengeId/flag', () => {
+  let user;
+  let challenge;
+
+  beforeEach(async () => {
+    const { group, groupLeader } = await createAndPopulateGroup({
+      groupDetails: {
+        name: 'TestParty',
+        type: 'party',
+        privacy: 'private',
+      },
+      members: 1,
+    });
+
+    user = groupLeader;
+
+    challenge = await generateChallenge(user, group);
+  });
+
+  it('returns an error when challenge is not found', async () => {
+    await expect(user.post(`/challenges/${generateUUID()}/flag`))
+      .to.eventually.be.rejected.and.eql({
+        code: 404,
+        error: 'NotFound',
+        message: t('challengeNotFound'),
+      });
+  });
+
+  it('flags a challenge', async () => {
+    const flagResult = await user.post(`/challenges/${challenge._id}/flag`);
+
+    expect(flagResult.challenge.flags[user._id]).to.equal(true);
+    expect(flagResult.challenge.flagCount).to.equal(1);
+  });
+
+  it('flags a challenge with a higher count when from an admin', async () => {
+    await user.update({ 'contributor.admin': true });
+
+    const flagResult = await user.post(`/challenges/${challenge._id}/flag`);
+
+    expect(flagResult.challenge.flags[user._id]).to.equal(true);
+    expect(flagResult.challenge.flagCount).to.equal(5);
+  });
+
+  it('returns an error when user tries to flag a challenge that is already flagged', async () => {
+    await user.post(`/challenges/${challenge._id}/flag`);
+
+    await expect(user.post(`/challenges/${challenge._id}/flag`))
+      .to.eventually.be.rejected.and.eql({
+        code: 404,
+        error: 'NotFound',
+        message: t('messageChallengeFlagAlreadyReported'),
+      });
+  });
+});
diff --git a/test/api/v3/integration/challenges/POST-challenge_flag_clear.test.js b/test/api/v3/integration/challenges/POST-challenge_flag_clear.test.js
new file mode 100644
index 0000000000..b1cfaaf667
--- /dev/null
+++ b/test/api/v3/integration/challenges/POST-challenge_flag_clear.test.js
@@ -0,0 +1,58 @@
+import { v4 as generateUUID } from 'uuid';
+import {
+  generateChallenge,
+  createAndPopulateGroup,
+  translate as t,
+} from '../../../../helpers/api-integration/v3';
+
+describe('POST /challenges/:challengeId/clearflags', () => {
+  let admin;
+  let nonAdmin;
+  let challenge;
+
+  beforeEach(async () => {
+    const { group, groupLeader, members } = await createAndPopulateGroup({
+      groupDetails: {
+        name: 'TestParty',
+        type: 'party',
+        privacy: 'private',
+      },
+      members: 1,
+    });
+
+    admin = groupLeader;
+    [nonAdmin] = members;
+
+    await admin.update({ 'permissions.moderator': true });
+
+    challenge = await generateChallenge(admin, group);
+    await admin.post(`/challenges/${challenge._id}/flag`);
+  });
+
+  it('returns error when non-admin attempts to clear flags', async () => {
+    await expect(nonAdmin.post(`/challenges/${generateUUID()}/clearflags`))
+      .to.eventually.be.rejected.and.eql({
+        code: 401,
+        error: 'NotAuthorized',
+        message: t('messageGroupChatAdminClearFlagCount'),
+      });
+  });
+
+  it('returns an error when challenge is not found', async () => {
+    await expect(admin.post(`/challenges/${generateUUID()}/clearflags`))
+      .to.eventually.be.rejected.and.eql({
+        code: 404,
+        error: 'NotFound',
+        message: t('challengeNotFound'),
+      });
+  });
+
+  it('clears flags and sets mod flag to false', async () => {
+    await nonAdmin.post(`/challenges/${challenge._id}/flag`);
+    const flagResult = await admin.post(`/challenges/${challenge._id}/clearflags`);
+
+    expect(flagResult.challenge.flagCount).to.eql(0);
+    expect(flagResult.challenge.flags).to.have.property(admin._id, false);
+    expect(flagResult.challenge.flags).to.have.property(nonAdmin._id, true);
+  });
+});
diff --git a/website/client/src/components/challenges/challengeDetail.vue b/website/client/src/components/challenges/challengeDetail.vue
index b86a2c28de..67c437c390 100644
--- a/website/client/src/components/challenges/challengeDetail.vue
+++ b/website/client/src/components/challenges/challengeDetail.vue
@@ -1,5 +1,6 @@
 <template>
   <div class="row">
+    <report-challenge-modal />
     <challenge-modal @updatedChallenge="updatedChallenge" />
     <leave-challenge-modal
       :challenge-id="challenge._id"
@@ -9,11 +10,27 @@
       :members="members"
       :challenge-id="challenge._id"
       :prize="challenge.prize"
+      :flag-count="challenge.flagCount"
     />
     <challenge-member-progress-modal :challenge-id="challenge._id" />
     <div class="col-12 col-md-8 standard-page">
       <div class="row">
         <div class="col-12 col-md-6">
+          <div
+            v-if="canViewFlags"
+            class="flagged"
+          >
+            <div
+              v-if="flaggedNotHidden"
+            >
+              {{ $t("flaggedNotHidden") }}
+            </div>
+            <div
+              v-else-if="flaggedAndHidden"
+            >
+              {{ $t("flaggedAndHidden") }}
+            </div>
+          </div>
           <h1 v-markdown="challenge.name"></h1>
           <div>
             <span class="mr-1 ml-0 d-block">
@@ -41,7 +58,7 @@
              createdBy string (helps with RTL languages)-->
             <!-- @TODO: Implement in V2 strong.margin-left
             (v-once).svg-icon.calendar-icon(v-html="icons.calendarIcon")
-| {{$t('endDate')}}
+            {{$t('endDate')}}
             // "endDate": "End Date: <% endDate %>",-->
             <!-- span {{challenge.endDate}}-->
           </div>
@@ -169,13 +186,16 @@
         v-if="isLeader || isAdmin"
         class="button-container"
       >
-        <button
-          v-once
-          class="btn btn-primary"
-          @click="cloneChallenge()"
-        >
-          {{ $t('clone') }}
-        </button>
+        <div>
+          <button
+            class="btn"
+            :disabled="flaggedAndHidden"
+            :class="flaggedAndHidden ? 'disabled btn-disabled' : 'btn-primary'"
+            @click="cloneChallenge()"
+          >
+            {{ $t('clone') }}
+          </button>
+        </div>
       </div>
       <div
         v-if="isLeader || isAdmin"
@@ -201,6 +221,17 @@
           {{ $t('endChallenge') }}
         </button>
       </div>
+      <div
+        class="button-container"
+      >
+        <button
+          v-once
+          class="btn btn-danger"
+          @click="reportChallenge()"
+        >
+          {{ $t('report') }}
+        </button>
+      </div>
       <div>
         <sidebar-section :title="$t('challengeSummary')">
           <p v-markdown="challenge.summary"></p>
@@ -249,6 +280,17 @@
     }
   }
 
+  .btn-disabled {
+    background-color: $gray-700;
+    color: $gray-50;
+    box-shadow: none;
+    cursor: arrow;
+
+    &:hover {
+      box-shadow: none;
+    }
+  }
+
   .calendar-icon {
     width: 12px;
     display: inline-block;
@@ -312,6 +354,15 @@
       margin-right: .5em;
     }
   }
+
+  .flagged {
+    margin-left: 0em;
+    color: $red-10;
+
+    span {
+      margin-left: 0em;
+    }
+  }
 </style>
 
 <script>
@@ -332,6 +383,7 @@ import challengeModal from './challengeModal';
 import challengeMemberProgressModal from './challengeMemberProgressModal';
 import challengeMemberSearchMixin from '@/mixins/challengeMemberSearch';
 import leaveChallengeModal from './leaveChallengeModal';
+import reportChallengeModal from './reportChallengeModal';
 import sidebarSection from '../sidebarSection';
 import userLink from '../userLink';
 import groupLink from '../groupLink';
@@ -350,6 +402,7 @@ export default {
   components: {
     closeChallengeModal,
     leaveChallengeModal,
+    reportChallengeModal,
     challengeModal,
     challengeMemberProgressModal,
     memberSearchDropdown,
@@ -401,6 +454,20 @@ export default {
     canJoin () {
       return !this.isMember;
     },
+    // canViewFlags should allow only moderators/admins to see flags
+    canViewFlags () {
+      const isModerator = this.hasPermission(this.user, 'moderator');
+      if (isModerator && this.challenge.flagCount > 0) return true;
+      return false;
+    },
+    // flaggedNotHidden should allow mods/admins & challenge owner to see flags
+    flaggedNotHidden () {
+      return this.challenge.flagCount === 1;
+    },
+    // flaggedAndHidden should only allow admin to see challenge & flags
+    flaggedAndHidden () {
+      return this.challenge.flagCount > 1;
+    },
   },
   watch: {
     'challenge.name': {
@@ -589,6 +656,14 @@ export default {
         challenge: this.challenge,
       });
     },
+    reportChallenge () {
+      this.$root.$emit('habitica::report-challenge', {
+        challenge: this.challenge,
+      });
+    },
+    async showCannotCloneModal () {
+      this.$root.$emit('bv::show::modal', 'cannot-clone-modal');
+    },
   },
 };
 </script>
diff --git a/website/client/src/components/challenges/challengeItem.vue b/website/client/src/components/challenges/challengeItem.vue
index 7bdf00bbc2..47099ed8e2 100644
--- a/website/client/src/components/challenges/challengeItem.vue
+++ b/website/client/src/components/challenges/challengeItem.vue
@@ -366,7 +366,6 @@
         }
       }
     }
-
   }
 </style>
 
diff --git a/website/client/src/components/challenges/closeChallengeModal.vue b/website/client/src/components/challenges/closeChallengeModal.vue
index a73d91fd87..6ce48f7968 100644
--- a/website/client/src/components/challenges/closeChallengeModal.vue
+++ b/website/client/src/components/challenges/closeChallengeModal.vue
@@ -2,7 +2,7 @@
   <div>
     <b-modal
       id="close-challenge-modal"
-      :title="$t('createGuild')"
+      :title="$t('endChallenge')"
       size="md"
     >
       <div
@@ -17,31 +17,42 @@
         </h2>
       </div>
       <div class="row text-center">
-        <div class="col-12">
-          <div class="support-habitica">
-            <!-- @TODO: Add challenge achievement badge here-->
+        <span
+          v-if="isFlagged"
+          class="col-12"
+        >
+          <div>{{ $t('cannotClose') }}</div>
+        </span>
+        <span
+          v-else
+          class="col-12"
+        >
+          <div class="col-12">
+            <div class="support-habitica">
+              <!-- @TODO: Add challenge achievement badge here-->
+            </div>
           </div>
-        </div>
-        <div class="col-12">
-          <strong v-once>{{ $t('selectChallengeWinnersDescription') }}</strong>
-        </div>
-        <div class="col-12">
-          <member-search-dropdown
-            :text="winnerText"
-            :members="members"
-            :challenge-id="challengeId"
-            @member-selected="selectMember"
-          />
-        </div>
-        <div class="col-12">
-          <button
-            v-once
-            class="btn btn-primary"
-            @click="closeChallenge"
-          >
-            {{ $t('awardWinners') }}
-          </button>
-        </div>
+          <div class="col-12">
+            <strong v-once>{{ $t('selectChallengeWinnersDescription') }}</strong>
+          </div>
+          <div class="col-12">
+            <member-search-dropdown
+              :text="winnerText"
+              :members="members"
+              :challenge-id="challengeId"
+              @member-selected="selectMember"
+            />
+          </div>
+          <div class="col-12">
+            <button
+              v-once
+              class="btn btn-primary"
+              @click="closeChallenge"
+            >
+              {{ $t('awardWinners') }}
+            </button>
+          </div>
+        </span>
         <div class="col-12">
           <hr>
           <div class="or">
@@ -123,7 +134,7 @@ export default {
   components: {
     memberSearchDropdown,
   },
-  props: ['challengeId', 'members', 'prize'],
+  props: ['challengeId', 'members', 'prize', 'flagCount'],
   data () {
     return {
       winner: {},
@@ -134,6 +145,9 @@ export default {
       if (!this.winner.profile) return this.$t('selectMember');
       return this.winner.profile.name;
     },
+    isFlagged () {
+      return this.flagCount > 0;
+    },
   },
   methods: {
     selectMember (member) {
diff --git a/website/client/src/components/challenges/reportChallengeModal.vue b/website/client/src/components/challenges/reportChallengeModal.vue
new file mode 100644
index 0000000000..463455e01b
--- /dev/null
+++ b/website/client/src/components/challenges/reportChallengeModal.vue
@@ -0,0 +1,273 @@
+<template>
+  <b-modal
+    id="report-challenge"
+    size="md"
+    :hide-footer="true"
+    :hide-header="true"
+  >
+    <div class="modal-body">
+      <div class="heading">
+        <h5
+          v-html="$t('abuseFlagModalHeading')"
+        >
+        </h5>
+      </div>
+      <div>
+        <span
+          class="svg-icon close-icon icon-16 color"
+          aria-hidden="true"
+          tabindex="0"
+          @click="close()"
+          @keypress.enter="close()"
+          v-html="icons.close"
+        ></span>
+      </div>
+      <blockquote>
+        <div
+          v-html="abuseObject.name"
+        >
+        </div>
+      </blockquote>
+      <div>
+        <span class="why-report">{{ $t('whyReportingChallenge') }}</span>
+        <textarea
+          v-model="reportComment"
+          class="form-control"
+          :placeholder="$t('whyReportingChallengePlaceholder')"
+        ></textarea>
+      </div>
+      <p
+        class="report-guidelines"
+        v-html="$t('abuseFlagModalBodyChallenge', abuseFlagModalBody)"
+      >
+      </p>
+    </div>
+    <div class="buttons text-center">
+      <div class="button-spacing">
+        <button
+          class="btn btn-danger"
+          :class="{disabled: !reportComment}"
+          @click="reportAbuse()"
+        >
+          {{ $t('report') }}
+        </button>
+      </div>
+      <div class="button-spacing">
+        <a
+          class="cancel-link"
+          @click.prevent="close()"
+        >
+          {{ $t('cancel') }}
+        </a>
+      </div>
+    </div>
+    <div
+      v-if="hasPermission(user, 'moderator')"
+      class="reset-flag-count d-flex justify-content-center align-items-middle"
+      @click="clearFlagCount()"
+    >
+      <div
+        v-once
+        class="svg-icon icon-16 color ml-auto mr-2 my-auto"
+        v-html="icons.report"
+      ></div>
+      <div
+        class="mr-auto my-auto"
+        @click="clearFlagCount()"
+      >
+        {{ $t('resetFlags') }}
+      </div>
+    </div>
+  </b-modal>
+</template>
+
+<style>
+  #report-challenge {
+    h5 {
+      color: #F23035;
+    }
+
+    .modal-header {
+      border: none;
+      padding-bottom: 0px;
+      padding-top: 12px;
+      height: 16px;
+      align-content: center;
+    }
+
+    .modal-content {
+      padding: 0px;
+    }
+  }
+</style>
+
+<style lang="scss" scoped>
+  @import '~@/assets/scss/colors.scss';
+
+  .modal-body {
+    padding: 0px 8px 0px 8px;
+  }
+
+  span.svg-icon.close-icon.icon-16 {
+    height: 16px;
+    width: 16px;
+    margin-top: -32px;
+    margin-right: -16px;
+  }
+
+  .close-icon {
+    color: $gray-300;
+    stroke-width: 0px;
+
+    &:hover {
+      color: $gray-200;
+    }
+  }
+
+  .heading h5 {
+    margin-bottom: 24px;
+    margin-top: 16px;
+    color: $red-10;
+    line-height: 1.4;
+  }
+
+  .why-report {
+    font-size: 1em;
+    font-weight: bold;
+    line-height: 1.71;
+    color: $gray-50;
+  }
+
+  .report-guidelines {
+    line-height: 1.71;
+    padding-bottom: 8px;
+  }
+
+   blockquote {
+     border-radius: 4px;
+     background-color: $gray-700;
+     padding: 8px 16px 8px 16px;
+     margin-top: 24px;
+     font-weight: bold;
+     color: $gray-10;
+     height: max-conent;;
+   }
+
+   textarea {
+     margin-top: 8px;
+     margin-bottom: 16px;
+     border-radius: 4px;
+     border: solid 1px $gray-400;
+     height: 64px;
+     font-size: 1em;
+   }
+
+   .btn {
+     width: 75px;
+   }
+
+   .buttons {
+     padding: 0 16px 0 16px;
+     margin-bottom: 16px;
+   }
+
+   .button-spacing {
+     margin-bottom: 16px;
+   }
+
+   .btn-danger.disabled {
+     background-color: $white;
+     color: $gray-50;
+     line-height: 1.71;
+     font-size: 1em;
+   }
+
+   a.cancel-link {
+     color: $purple-300;
+   }
+
+   .reset-flag-count {
+     margin: 16px -16px -16px -16px;
+     height: 48px;
+     color: $maroon-50;
+     background-color: rgba(255, 182, 184, 0.25);
+     border-bottom-left-radius: 8px;
+     border-bottom-right-radius: 8px;
+     justify-content: center;
+     cursor: pointer;
+
+     &:hover {
+      text-decoration: underline;
+     }
+   }
+</style>
+
+<script>
+import { mapState } from '@/libs/store';
+import notifications from '@/mixins/notifications';
+import { userStateMixin } from '../../mixins/userState';
+import markdownDirective from '@/directives/markdown';
+import svgClose from '@/assets/svg/close.svg';
+import svgReport from '@/assets/svg/report.svg';
+
+export default {
+  directives: {
+    markdown: markdownDirective,
+  },
+  mixins: [notifications, userStateMixin],
+  data () {
+    const abuseFlagModalBody = {
+      firstLinkStart: '<a href="/static/community-guidelines" target="_blank">',
+      secondLinkStart: '<a href="/static/terms" target="_blank">',
+      linkEnd: '</a>',
+    };
+
+    return {
+      abuseFlagModalBody,
+      abuseObject: '',
+      groupId: '',
+      reportComment: '',
+      icons: Object.freeze({
+        close: svgClose,
+        report: svgReport,
+      }),
+    };
+  },
+  computed: {
+    ...mapState({ user: 'user.data' }),
+  },
+  created () {
+    this.$root.$on('habitica::report-challenge', this.handleReport);
+  },
+  destroyed () {
+    this.$root.$off('habitica::report-challenge', this.handleReport);
+  },
+  methods: {
+    close () {
+      this.$root.$emit('bv::hide::modal', 'report-challenge');
+    },
+    async reportAbuse () {
+      if (!this.reportComment) return;
+      this.$store.dispatch('challenges:flag', {
+        challengeId: this.abuseObject.id,
+        comment: this.reportComment,
+      }).then(() => {
+        this.text(this.$t('abuseReported'));
+        this.close();
+      }).catch(() => {});
+    },
+    async clearFlagCount () {
+      await this.$store.dispatch('challenges:clearFlagCount', {
+        challengeId: this.abuseObject.id,
+      });
+      this.close();
+    },
+    handleReport (data) {
+      if (!data.challenge) return;
+      this.abuseObject = data.challenge;
+      this.reportComment = '';
+      this.$root.$emit('bv::show::modal', 'report-challenge');
+    },
+  },
+};
+</script>
diff --git a/website/client/src/store/actions/challenges.js b/website/client/src/store/actions/challenges.js
index 41406e3d61..a32173ceba 100644
--- a/website/client/src/store/actions/challenges.js
+++ b/website/client/src/store/actions/challenges.js
@@ -97,3 +97,15 @@ export async function selectChallengeWinner (store, payload) {
 
   return response.data.data;
 }
+
+export async function flag (store, payload) {
+  const response = await axios.post(`/api/v3/challenges/${payload.challengeId}/flag`, {
+    comment: payload.comment,
+  });
+  return response.data.data;
+}
+
+export async function clearFlagCount (store, payload) {
+  const response = await axios.post(`/api/v3/challenges/${payload.challengeId}/clearflags`);
+  return response.data.data;
+}
diff --git a/website/common/locales/en/challenge.json b/website/common/locales/en/challenge.json
index 375df7af7b..4fca247ad5 100644
--- a/website/common/locales/en/challenge.json
+++ b/website/common/locales/en/challenge.json
@@ -88,13 +88,23 @@
   "summaryRequired": "Summary is required",
   "summaryTooLong": "Summary is too long",
   "descriptionRequired": "Description is required",
-  "locationRequired": "Location of challenge is required ('Add to')",
+  "locationRequired": "Location of Challenge is required ('Add to')",
   "categoiresRequired": "One or more categories must be selected",
   "viewProgressOf": "View Progress Of",
   "viewProgress": "View Progress",
   "selectMember": "Select Member",
-  "confirmKeepChallengeTasks": "Do you want to keep challenge tasks?",
+  "confirmKeepChallengeTasks": "Do you want to keep Challenge tasks?",
   "selectParticipant": "Select a Participant",
   "yourReward": "Your Reward",
-  "wonChallengeDesc": "<%= challengeName %> selected you as the winner! Your win has been recorded in your Achievements."
+  "wonChallengeDesc": "<%= challengeName %> selected you as the winner! Your win has been recorded in your Achievements.",
+  "messageChallengeFlagAlreadyReported": "You have already reported this Challenge.",
+  "flaggedNotHidden": "Challenge flagged once, not hidden",
+  "flaggedAndHidden": "Challenge flagged and hidden",
+  "resetFlagCount": "Reset Flag Count",
+  "whyReportingChallenge": "Why are you reporting this Challenge?",
+  "whyReportingChallengePlaceholder": "Reason for report",
+  "abuseFlagModalBodyChallenge": "You should only report a Challenge that violates the <%= firstLinkStart %>Community Guidelines<%= linkEnd %> and/or <%= secondLinkStart %>Terms of Service<%= linkEnd %>. Submitting a false report is a violation of Habitica's Community Guidelines.",
+  "cannotClose": "This Challenge cannot be closed because one or more players have reported it as inappropriate. A staff members will contact you shortly with instructions. If over 48 hours have passed and you have not heard from them, please email admin@habitica.com for assistance.",
+  "cannotClone": "This Challenge cannot be cloned because one or more players have reported it as inappropriate. A staff member will contact you shortly with instructions. If over 48 hours have passed and you have not heard from them, please email admin@habitica.com for assistance.",
+  "resetFlags": "Reset Flags"
 }
diff --git a/website/common/locales/en/groups.json b/website/common/locales/en/groups.json
index 89f3f443da..bc7c6eee03 100644
--- a/website/common/locales/en/groups.json
+++ b/website/common/locales/en/groups.json
@@ -103,7 +103,7 @@
   "cannotSendGemsToYourself": "Cannot send gems to yourself. Try a subscription instead.",
   "badAmountOfGemsToSend": "Amount must be within 1 and your current number of gems.",
   "report": "Report",
-  "abuseFlagModalHeading": "Report a Violation",
+  "abuseFlagModalHeading": "Report Violation",
   "abuseFlagModalBody": "Are you sure you want to report this post? You should <strong>only</strong> report a post that violates the <%= firstLinkStart %>Community Guidelines<%= linkEnd %> and/or <%= secondLinkStart %>Terms of Service<%= linkEnd %>. Inappropriately reporting a post is a violation of the Community Guidelines and may give you an infraction.",
   "abuseReported": "Thank you for reporting this violation. The moderators have been notified.",
   "pmReported": "Thank you for reporting this message.",
diff --git a/website/server/controllers/api-v3/challenges.js b/website/server/controllers/api-v3/challenges.js
index 7db05352c2..dcfc372f3d 100644
--- a/website/server/controllers/api-v3/challenges.js
+++ b/website/server/controllers/api-v3/challenges.js
@@ -20,7 +20,6 @@ import csvStringify from '../../libs/csvStringify';
 import {
   createTasks,
 } from '../../libs/tasks';
-
 import {
   addUserJoinChallengeNotification,
   getChallengeGroupResponse,
@@ -29,8 +28,12 @@ import {
   createChallengeQuery,
 } from '../../libs/challenges';
 import apiError from '../../libs/apiError';
-
 import common from '../../../common';
+import {
+  clearFlags,
+  flagChallenge,
+  notifyOfFlaggedChallenge,
+} from '../../libs/challenges/reporting';
 
 const { MAX_SUMMARY_SIZE_FOR_CHALLENGES } = common.constants;
 
@@ -366,7 +369,7 @@ api.leaveChallenge = {
  * @apiParam (Query) {Number} page This parameter can be used to specify the page number
                                    for the user challenges result (the initial page is number 0).
  * @apiParam (Query) {String} [member] If set to `true` it limits results to challenges where the
-                                       user is a member.
+                                       user is a member, or the user owns the challenge.
  * @apiParam (Query) {String} [owned] If set to `owned` it limits results to challenges owned
                                       by the user. If set to `not_owned` it limits results
                                       to challenges not owned by the user.
@@ -394,10 +397,30 @@ api.getUserChallenges = {
     if (validationErrors) throw validationErrors;
 
     const CHALLENGES_PER_PAGE = 10;
-    const { page } = req.query;
-
+    const {
+      categories,
+      member,
+      owned,
+      page,
+      search,
+    } = req.query;
     const { user } = res.locals;
 
+    const query = {
+      $and: [],
+    };
+
+    if (!user.hasPermission('moderator')) {
+      query.$and.push(
+        {
+          $or: [
+            { flagCount: { $not: { $gt: 1 } } },
+            { leader: user._id },
+          ],
+        },
+      );
+    }
+
     // Challenges the user owns
     const orOptions = [{ leader: user._id }];
 
@@ -407,7 +430,7 @@ api.getUserChallenges = {
     }
 
     // Challenges in groups user is a member of, plus public challenges
-    if (!req.query.member) {
+    if (!member) {
       const userGroups = await Group.getGroups({
         user,
         types: ['party', 'guilds', 'tavern'],
@@ -417,33 +440,29 @@ api.getUserChallenges = {
         group: { $in: userGroupIds },
       });
     }
-
-    const query = {
-      $and: [{ $or: orOptions }],
-    };
-
-    const { owned } = req.query;
-    if (owned) {
-      if (owned === 'not_owned') {
-        query.$and.push({ leader: { $ne: user._id } });
-      }
-
-      if (owned === 'owned') {
-        query.$and.push({ leader: user._id });
-      }
+    if (owned === 'not_owned') {
+      query.leader = { $ne: user._id }; // Show only Challenges user does not own
+    } else if (owned === 'owned') {
+      query.leader = user._id; // Show only Challenges user owns
+    } else {
+      orOptions.push(
+        { leader: user._id }, // Additionally show Challenges user owns
+      );
     }
 
-    if (req.query.search) {
+    query.$and.push({ $or: orOptions });
+
+    if (search) {
       const searchOr = { $or: [] };
-      const searchWords = _.escapeRegExp(req.query.search).split(' ').join('|');
+      const searchWords = _.escapeRegExp(search).split(' ').join('|');
       const searchQuery = { $regex: new RegExp(`${searchWords}`, 'i') };
       searchOr.$or.push({ name: searchQuery });
       searchOr.$or.push({ description: searchQuery });
       query.$and.push(searchOr);
     }
 
-    if (req.query.categories) {
-      const categorySlugs = req.query.categories.split(',');
+    if (categories) {
+      const categorySlugs = categories.split(',');
       query.categories = { $elemMatch: { slug: { $in: categorySlugs } } };
     }
 
@@ -502,7 +521,7 @@ api.getGroupChallenges = {
   url: '/challenges/groups/:groupId',
   middlewares: [authWithHeaders({
     // Some fields (including _id) are always loaded (see middlewares/auth)
-    userFieldsToInclude: ['party', 'guilds'], // Some fields are always loaded (see middlewares/auth)
+    userFieldsToInclude: ['party', 'guilds', 'contributor'], // Some fields are always loaded (see middlewares/auth)
   })],
   async handler (req, res) {
     const { user } = res.locals;
@@ -524,7 +543,18 @@ api.getGroupChallenges = {
       // .populate('leader', nameFields)
       .exec();
 
-    const resChals = challenges.map(challenge => (new Challenge(challenge)).toJSON());
+    const resChals = challenges.map(challenge => {
+      // filter out challenges that the non-admin user isn't participating in, nor created
+      const nonParticipant = !user.challenges
+        || (user.challenges
+        && user.challenges.findIndex(cId => cId === challenge._id) === -1);
+      const isFlaggedForNonAdminUser = challenge.flagCount > 1
+        && !user.hasPermission('moderator')
+        && nonParticipant
+        && challenge.leader !== user._id;
+
+      return isFlaggedForNonAdminUser ? null : (new Challenge(challenge)).toJSON();
+    }).filter(challenge => !!challenge);
 
     // Instead of populate we make a find call manually because of https://github.com/Automattic/mongoose/issues/3833
     await Promise.all(resChals.map((chal, index) => User
@@ -573,6 +603,15 @@ api.getChallenge = {
 
     if (!challenge) throw new NotFound(res.t('challengeNotFound'));
 
+    const nonParticipant = !user.challenges
+      || (user.challenges
+      && user.challenges.findIndex(cId => cId === challenge._id) === -1);
+    const isFlaggedForNonAdminUser = challenge.flagCount > 1
+      && !user.hasPermission('moderator')
+      && nonParticipant
+      && challenge.leader !== user._id;
+    if (isFlaggedForNonAdminUser) throw new NotFound(res.t('challengeNotFound'));
+
     // Fetching basic group data
     const group = await Group.getGroup({
       user, groupId: challenge.group, fields: `${basicGroupFields} purchased`,
@@ -828,6 +867,15 @@ api.selectChallengeWinner = {
     if (!challenge) throw new NotFound(res.t('challengeNotFound'));
     if (!challenge.canModify(user)) throw new NotAuthorized(res.t('onlyLeaderDeleteChal'));
 
+    const nonParticipant = !user.challenges
+      || (user.challenges
+      && user.challenges.findIndex(cId => cId === challenge._id) === -1);
+    const isFlaggedForNonAdminUser = challenge.flagCount > 1
+      && !user.hasPermission('moderator')
+      && nonParticipant
+      && challenge.leader !== user._id;
+    if (isFlaggedForNonAdminUser) throw new NotFound(res.t('challengeNotFound'));
+
     const winner = await User.findOne({ _id: req.params.winnerId }).exec();
     if (!winner || winner.challenges.indexOf(challenge._id) === -1) throw new NotFound(res.t('winnerNotFound', { userId: req.params.winnerId }));
 
@@ -877,6 +925,15 @@ api.cloneChallenge = {
     const challengeToClone = await Challenge.findOne({ _id: req.params.challengeId }).exec();
     if (!challengeToClone) throw new NotFound(res.t('challengeNotFound'));
 
+    const nonParticipant = !user.challenges
+      || (user.challenges
+      && user.challenges.findIndex(cId => cId === challengeToClone._id) === -1);
+    const isFlaggedForNonAdminUser = challengeToClone.flagCount > 1
+      && !user.hasPermission('moderator')
+      && nonParticipant
+      && challengeToClone.leader !== user._id;
+    if (isFlaggedForNonAdminUser) throw new NotFound(res.t('challengeNotFound'));
+
     const { savedChal } = await createChallenge(user, req, res);
 
     const challengeTaskIds = [
@@ -910,4 +967,74 @@ api.cloneChallenge = {
   },
 };
 
+/**
+ * @api {post} /api/v3/challenges/:challengeId/flag Flag a challenge
+ * @apiName FlagChallenge
+ * @apiGroup Challenge
+ *
+ * @apiParam (Path) {UUID} challengeId The _id for the challenge to flag
+ * @apiParam (Body) {String} [comment] Why the message was flagged
+ *
+ * @apiSuccess {Object} data The flagged challenge message
+ *
+ * @apiUse ChallengeNotFound
+ */
+api.flagChallenge = {
+  method: 'POST',
+  url: '/challenges/:challengeId/flag',
+  middlewares: [authWithHeaders()],
+  async handler (req, res) {
+    const { user } = res.locals;
+
+    req.checkParams('challengeId', res.t('challengeIdRequired')).notEmpty().isUUID();
+
+    const validationErrors = req.validationErrors();
+    if (validationErrors) throw validationErrors;
+
+    const challenge = await Challenge.findOne({ _id: req.params.challengeId }).exec();
+    if (!challenge) throw new NotFound(res.t('challengeNotFound'));
+
+    await flagChallenge(challenge, user, res);
+    await notifyOfFlaggedChallenge(challenge, user, req.body.comment);
+
+    res.respond(200, { challenge });
+  },
+};
+
+/**
+ * @api {post} /api/v3/challenges/:challengeId/clearflags Clears flags on a challenge
+ * @apiName ClearFlagsChallenge
+ * @apiGroup Challenge
+ *
+ * @apiParam (Path) {UUID} challengeId The _id for the challenge to clear flags from
+ *
+ * @apiSuccess {Object} data The flagged challenge message
+ *
+ * @apiUse ChallengeNotFound
+ */
+api.clearFlagsChallenge = {
+  method: 'POST',
+  url: '/challenges/:challengeId/clearflags',
+  middlewares: [authWithHeaders()],
+  async handler (req, res) {
+    const { user } = res.locals;
+
+    req.checkParams('challengeId', res.t('challengeIdRequired')).notEmpty().isUUID();
+
+    const validationErrors = req.validationErrors();
+    if (validationErrors) throw validationErrors;
+
+    if (!user.hasPermission('moderator')) {
+      throw new NotAuthorized(res.t('messageGroupChatAdminClearFlagCount'));
+    }
+
+    const challenge = await Challenge.findOne({ _id: req.params.challengeId }).exec();
+    if (!challenge) throw new NotFound(res.t('challengeNotFound'));
+
+    await clearFlags(challenge, user);
+
+    res.respond(200, { challenge });
+  },
+};
+
 export default api;
diff --git a/website/server/libs/challenges/index.js b/website/server/libs/challenges/index.js
index 282a348ad4..98cc7d9425 100644
--- a/website/server/libs/challenges/index.js
+++ b/website/server/libs/challenges/index.js
@@ -91,6 +91,11 @@ export async function createChallenge (user, req, res) {
     }
   }
 
+  if (challenge.flagCount > 0) {
+    challenge.flagCount = 0;
+    challenge.flags = {};
+  }
+
   const results = await Promise.all([challenge.save({
     validateBeforeSave: false, // already validated
   }), group.save(), user.save()]);
diff --git a/website/server/libs/challenges/reporting.js b/website/server/libs/challenges/reporting.js
new file mode 100644
index 0000000000..3b181fc282
--- /dev/null
+++ b/website/server/libs/challenges/reporting.js
@@ -0,0 +1,82 @@
+import nconf from 'nconf';
+import { getUserInfo, sendTxn, getGroupUrl } from '../email';
+import { NotFound } from '../errors';
+import * as slack from '../slack';
+
+const FLAG_REPORT_EMAILS = nconf.get('FLAG_REPORT_EMAIL').split(',').map(email => ({ email, canSend: true }));
+
+export async function notifyOfFlaggedChallenge (challenge, user, userComment) {
+  const reporterEmailContent = getUserInfo(user, ['email']).email;
+
+  const emailVariables = [
+    { name: 'CHALLENGE_NAME', content: challenge.name },
+    { name: 'CHALLENGE_ID', content: challenge._id },
+
+    { name: 'REPORTER_USERNAME', content: user.profile.name },
+    { name: 'REPORTER_UUID', content: user._id },
+    { name: 'REPORTER_EMAIL', content: reporterEmailContent },
+    { name: 'REPORTER_MODAL_URL', content: `/static/front/#?memberId=${user._id}` },
+    { name: 'REPORTER_COMMENT', content: userComment || '' },
+
+    { name: 'AUTHOR_UUID', content: challenge.leader._id },
+    { name: 'AUTHOR_MODAL_URL', content: `/static/front/#?memberId=${challenge.leader._id}` },
+  ];
+
+  sendTxn(FLAG_REPORT_EMAILS, 'flag-report-to-mods', emailVariables);
+
+  slack.sendChallengeFlagNotification({
+    flagger: user,
+    challenge,
+    userComment,
+  });
+}
+
+export async function flagChallenge (challenge, user, res) {
+  if (challenge.flags[user._id] && !user.contributor.admin) throw new NotFound(res.t('messageChallengeFlagAlreadyReported'));
+
+  challenge.flags[user._id] = true;
+  challenge.markModified('flags');
+
+  if (user.contributor.admin) {
+    // Arbitrary amount, higher than 2
+    challenge.flagCount = 5;
+  } else {
+    challenge.flagCount += 1;
+  }
+
+  await challenge.save();
+}
+
+export async function clearFlags (challenge, user) {
+  challenge.flagCount = 0;
+  if (user.contributor.admin) { // let's get this to a proper "permissions" check later
+    challenge.flags = {};
+    challenge.markModified('flags');
+  } else if (challenge.flags[user._id]) {
+    challenge.flags[user._id] = false;
+    challenge.markModified('flags');
+  }
+  await challenge.save();
+
+  const adminEmailContent = getUserInfo(user, ['email']).email;
+  const challengeUrl = `/challenges/${challenge._id}`;
+
+  const groupUrl = getGroupUrl({ _id: challenge.group, type: 'guild' });
+
+  sendTxn(FLAG_REPORT_EMAILS, 'unflag-report-to-mods', [
+    { name: 'ADMIN_USERNAME', content: user.profile.name },
+    { name: 'ADMIN_UUID', content: user._id },
+    { name: 'ADMIN_EMAIL', content: adminEmailContent },
+    { name: 'ADMIN_MODAL_URL', content: `/static/front/#?memberId=${user._id}` },
+
+    { name: 'AUTHOR_UUID', content: challenge.leader },
+    { name: 'AUTHOR_EMAIL', content: adminEmailContent },
+    { name: 'AUTHOR_MODAL_URL', content: `/static/front/#?memberId=${challenge.leader}` },
+
+    { name: 'CHALLENGE_NAME', content: challenge.name },
+    { name: 'CHALLENGE_ID', content: challenge._id },
+    { name: 'CHALLENGE_URL', content: challengeUrl },
+
+    { name: 'GROUP_URL', content: groupUrl },
+  ]);
+}
diff --git a/website/server/libs/slack.js b/website/server/libs/slack.js
index 0f2997a239..69c072e2a4 100644
--- a/website/server/libs/slack.js
+++ b/website/server/libs/slack.js
@@ -176,6 +176,41 @@ function sendInboxFlagNotification ({
     .catch(err => logger.error(err, 'Error while sending flag data to Slack.'));
 }
 
+function sendChallengeFlagNotification ({
+  flagger,
+  challenge,
+  userComment,
+}) {
+  if (SKIP_FLAG_METHODS) {
+    return;
+  }
+  const titleLink = `${BASE_URL}/challenges/${challenge.id}`;
+  const title = `Flag in challenge "${challenge.name}"`;
+  let text = `${flagger.profile.name} (${flagger.id}; language: ${flagger.preferences.language}) flagged a challenge`;
+  const footer = '';
+
+  if (userComment) {
+    text += ` and commented: ${userComment}`;
+  }
+
+  const challengeText = challenge.summary;
+
+  flagSlack.send({
+    text,
+    attachments: [{
+      fallback: 'Flag Message',
+      color: 'danger',
+      title,
+      title_link: titleLink,
+      text: challengeText,
+      footer,
+      mrkdwn_in: [
+        'text',
+      ],
+    }],
+  });
+}
+
 function sendProfileFlagNotification ({
   reporter,
   flaggedUser,
@@ -339,6 +374,7 @@ function sendSlurNotification ({
 export {
   sendFlagNotification,
   sendInboxFlagNotification,
+  sendChallengeFlagNotification,
   sendProfileFlagNotification,
   sendSubscriptionNotification,
   sendShadowMutedPostNotification,
diff --git a/website/server/models/challenge.js b/website/server/models/challenge.js
index e5a7814558..3993d66e00 100644
--- a/website/server/models/challenge.js
+++ b/website/server/models/challenge.js
@@ -46,6 +46,8 @@ const schema = new Schema({
     slug: { $type: String },
     name: { $type: String },
   }],
+  flags: { $type: mongoose.Schema.Types.Mixed, default: {} },
+  flagCount: { $type: Number, default: 0, min: 0 },
 }, {
   strict: true,
   minimize: false, // So empty objects are returned