diff --git a/src/index.js b/src/index.js
index 916056fe0..77c56336d 100644
--- a/src/index.js
+++ b/src/index.js
@@ -20,6 +20,7 @@ module.exports = {
   DataStore: require('./stores/DataStore'),
   DiscordAPIError: require('./rest/DiscordAPIError'),
   HTTPError: require('./rest/HTTPError'),
+  MessageFlags: require('./util/MessageFlags'),
   Permissions: require('./util/Permissions'),
   Speaking: require('./util/Speaking'),
   Snowflake: require('./util/Snowflake'),
diff --git a/src/structures/Message.js b/src/structures/Message.js
index 5b6cc4754..8a9df07ea 100644
--- a/src/structures/Message.js
+++ b/src/structures/Message.js
@@ -13,6 +13,7 @@ const Permissions = require('../util/Permissions');
 const Base = require('./Base');
 const { Error, TypeError } = require('../errors');
 const APIMessage = require('./APIMessage');
+const MessageFlags = require('../util/MessageFlags');
 
 /**
  * Represents a message on Discord.
@@ -81,7 +82,9 @@ class Message extends Base {
 
     /**
      * A random number or string used for checking message delivery
-     * @type {string}
+     * <warn>This is only received after the message was sent successfully, and
+     * lost if re-fetched</warn>
+     * @type {?string}
      */
     this.nonce = data.nonce;
 
@@ -89,7 +92,7 @@ class Message extends Base {
      * Whether or not this message was sent by Discord, not actually a user (e.g. pin notifications)
      * @type {boolean}
      */
-    this.system = data.type === 6;
+    this.system = data.type !== 0;
 
     /**
      * A list of embeds in the message - e.g. YouTube Player
@@ -137,7 +140,7 @@ class Message extends Base {
      * All valid mentions that the message contains
      * @type {MessageMentions}
      */
-    this.mentions = new Mentions(this, data.mentions, data.mention_roles, data.mention_everyone);
+    this.mentions = new Mentions(this, data.mentions, data.mention_roles, data.mention_everyone, data.mention_channels);
 
     /**
      * ID of the webhook that sent the message, if applicable
@@ -172,6 +175,30 @@ class Message extends Base {
     } else if (data.member && this.guild && this.author) {
       this.guild.members.add(Object.assign(data.member, { user: this.author }));
     }
+
+    /**
+     * Flags that are applied to the message
+     * @type {Readonly<MessageFlags>}
+     */
+    this.flags = new MessageFlags(data.flags).freeze();
+
+    /**
+     * Reference data sent in a crossposted message.
+     * @typedef {Object} MessageReference
+     * @property {string} channelID ID of the channel the message was crossposted from
+     * @property {?string} guildID ID of the guild the message was crossposted from
+     * @property {?string} messageID ID of the message that was crossposted
+     */
+
+    /**
+     * Message reference data
+     * @type {?MessageReference}
+     */
+    this.reference = data.message_reference ? {
+      channelID: data.message_reference.channel_id,
+      guildID: data.message_reference.guild_id,
+      messageID: data.message_reference.message_id,
+    } : null;
   }
 
   /**
@@ -214,8 +241,11 @@ class Message extends Base {
       this,
       'mentions' in data ? data.mentions : this.mentions.users,
       'mentions_roles' in data ? data.mentions_roles : this.mentions.roles,
-      'mention_everyone' in data ? data.mention_everyone : this.mentions.everyone
+      'mention_everyone' in data ? data.mention_everyone : this.mentions.everyone,
+      'mention_channels' in data ? data.mention_channels : this.mentions.crosspostedChannels
     );
+
+    this.flags = new MessageFlags('flags' in data ? data.flags : 0).freeze();
   }
 
   /**
diff --git a/src/structures/MessageMentions.js b/src/structures/MessageMentions.js
index 610c8c127..9b17685f6 100644
--- a/src/structures/MessageMentions.js
+++ b/src/structures/MessageMentions.js
@@ -3,12 +3,13 @@
 const Collection = require('../util/Collection');
 const Util = require('../util/Util');
 const GuildMember = require('./GuildMember');
+const { ChannelTypes } = require('../util/Constants');
 
 /**
  * Keeps track of mentions in a {@link Message}.
  */
 class MessageMentions {
-  constructor(message, users, roles, everyone) {
+  constructor(message, users, roles, everyone, crosspostedChannels) {
     /**
      * The client the message is from
      * @type {Client}
@@ -86,6 +87,39 @@ class MessageMentions {
      * @private
      */
     this._channels = null;
+
+    /**
+     * Crossposted channel data.
+     * @typedef {Object} CrosspostedChannel
+     * @property {string} channelID ID of the mentioned channel
+     * @property {string} guildID ID of the guild that has the channel
+     * @property {string} type Type of the channel
+     * @property {string} name The name of the channel
+     */
+
+    if (crosspostedChannels) {
+      if (crosspostedChannels instanceof Collection) {
+        /**
+         * A collection of crossposted channels
+         * @type {Collection<Snowflake, CrosspostedChannel>}
+         */
+        this.crosspostedChannels = new Collection(crosspostedChannels);
+      } else {
+        this.crosspostedChannels = new Collection();
+        const channelTypes = Object.keys(ChannelTypes);
+        for (const d of crosspostedChannels) {
+          const type = channelTypes[d.type];
+          this.crosspostedChannels.set(d.id, {
+            channelID: d.id,
+            guildID: d.guild_id,
+            type: type ? type.toLowerCase() : 'unknown',
+            name: d.name,
+          });
+        }
+      }
+    } else {
+      this.crosspostedChannels = new Collection();
+    }
   }
 
   /**
diff --git a/src/util/Constants.js b/src/util/Constants.js
index 9d742e784..7bb3bb50e 100644
--- a/src/util/Constants.js
+++ b/src/util/Constants.js
@@ -386,6 +386,7 @@ exports.WSEvents = keyMirror([
  * * USER_PREMIUM_GUILD_SUBSCRIPTION_TIER_1
  * * USER_PREMIUM_GUILD_SUBSCRIPTION_TIER_2
  * * USER_PREMIUM_GUILD_SUBSCRIPTION_TIER_3
+ * * CHANNEL_FOLLOW_ADD
  * @typedef {string} MessageType
  */
 exports.MessageTypes = [
@@ -401,6 +402,7 @@ exports.MessageTypes = [
   'USER_PREMIUM_GUILD_SUBSCRIPTION_TIER_1',
   'USER_PREMIUM_GUILD_SUBSCRIPTION_TIER_2',
   'USER_PREMIUM_GUILD_SUBSCRIPTION_TIER_3',
+  'CHANNEL_FOLLOW_ADD',
 ];
 
 /**
diff --git a/src/util/MessageFlags.js b/src/util/MessageFlags.js
new file mode 100644
index 000000000..b1c86b7d6
--- /dev/null
+++ b/src/util/MessageFlags.js
@@ -0,0 +1,25 @@
+'use strict';
+
+const BitField = require('./BitField');
+
+/**
+ * Data structure that makes it easy to interact with an {@link Message#flags} bitfield.
+ * @extends {BitField}
+ */
+class MessageFlags extends BitField {}
+
+/**
+ * Numeric message flags. All available properties:
+ * * `CROSSPOSTED`
+ * * `IS_CROSSPOST`
+ * * `SUPPRESS_EMBEDS`
+ * @type {Object}
+ * @see {@link https://discordapp.com/developers/docs/resources/channel#message-object-message-flags}
+ */
+MessageFlags.FLAGS = {
+  CROSSPOSTED: 1 << 0,
+  IS_CROSSPOST: 1 << 1,
+  SUPPRESS_EMBEDS: 1 << 2,
+};
+
+module.exports = MessageFlags;
diff --git a/typings/index.d.ts b/typings/index.d.ts
index 4f03ef11d..cb08e2ffe 100644
--- a/typings/index.d.ts
+++ b/typings/index.d.ts
@@ -1,3 +1,14 @@
+declare enum ChannelType {
+	text,
+	dm,
+	voice,
+	group,
+	category,
+	news,
+	store,
+	unknown
+}
+
 declare module 'discord.js' {
 	import BaseCollection from '@discordjs/collection';
 	import { EventEmitter } from 'events';
@@ -125,7 +136,7 @@ declare module 'discord.js' {
 		public readonly createdTimestamp: number;
 		public deleted: boolean;
 		public id: Snowflake;
-		public type: 'dm' | 'text' | 'voice' | 'category' | 'news' | 'store' | 'unknown';
+		public type: keyof typeof ChannelType;
 		public delete(reason?: string): Promise<Channel>;
 		public fetch(): Promise<Channel>;
 		public toString(): string;
@@ -914,12 +925,17 @@ declare module 'discord.js' {
 		public toString(): string;
 	}
 
+	export class MessageFlags extends BitField<MessageFlagsString> {
+		public static FLAGS: Record<MessageFlagsString, number>;
+		public static resolve(bit?: BitFieldResolvable<MessageFlagsString>): number;
+	}
+
 	export class Message extends Base {
 		constructor(client: Client, data: object, channel: TextChannel | DMChannel);
 		private _edits: Message[];
 		private patch(data: object): void;
 
-		public activity: GroupActivity | null;
+		public activity: MessageActivity | null;
 		public application: ClientApplication | null;
 		public attachments: Collection<Snowflake, MessageAttachment>;
 		public author: User | null;
@@ -939,7 +955,7 @@ declare module 'discord.js' {
 		public id: Snowflake;
 		public readonly member: GuildMember | null;
 		public mentions: MessageMentions;
-		public nonce: string;
+		public nonce: string | null;
 		public readonly partial: boolean;
 		public readonly pinnable: boolean;
 		public pinned: boolean;
@@ -949,6 +965,8 @@ declare module 'discord.js' {
 		public type: MessageType;
 		public readonly url: string;
 		public webhookID: Snowflake | null;
+		public flags: Readonly<MessageFlags>;
+		public reference: MessageReference | null;
 		public awaitReactions(filter: CollectorFilter, options?: AwaitReactionsOptions): Promise<Collection<Snowflake, MessageReaction>>;
 		public createReactionCollector(filter: CollectorFilter, options?: ReactionCollectorOptions): ReactionCollector;
 		public delete(options?: { timeout?: number, reason?: string }): Promise<Message>;
@@ -1054,6 +1072,7 @@ declare module 'discord.js' {
 		public readonly members: Collection<Snowflake, GuildMember> | null;
 		public roles: Collection<Snowflake, Role>;
 		public users: Collection<Snowflake, User>;
+		public crosspostedChannels: Collection<Snowflake, CrosspostedChannel>;
 		public toJSON(): object;
 
 		public static CHANNELS_PATTERN: RegExp;
@@ -1886,6 +1905,10 @@ declare module 'discord.js' {
 		| 'LISTENING'
 		| 'WATCHING';
 
+	type MessageFlagsString = 'CROSSPOSTED'
+		| 'IS_CROSSPOST'
+		| 'SUPPRESS_EMBEDS';
+
 	interface APIErrror {
 		UNKNOWN_ACCOUNT: number;
 		UNKNOWN_APPLICATION: number;
@@ -2128,11 +2151,17 @@ declare module 'discord.js' {
 		name?: string;
 	}
 
-	interface GroupActivity {
+	interface MessageActivity {
 		partyID: string;
 		type: number;
 	}
 
+	interface MessageReference {
+		channelID: string;
+		guildID: string;
+		messageID: string | null;
+	}
+
 	type GuildAuditLogsAction = keyof GuildAuditLogsActions;
 
 	interface GuildAuditLogsActions {
@@ -2196,7 +2225,7 @@ declare module 'discord.js' {
 	interface GuildCreateChannelOptions {
 		permissionOverwrites?: OverwriteResolvable[] | Collection<Snowflake, OverwriteResolvable>;
 		topic?: string;
-		type?: 'text' | 'voice' | 'category';
+		type?: Exclude<keyof typeof ChannelType, 'dm' | 'group' | 'unknown'>;
 		nsfw?: boolean;
 		parent?: ChannelResolvable;
 		bitrate?: number;
@@ -2373,7 +2402,8 @@ declare module 'discord.js' {
 		| 'USER_PREMIUM_GUILD_SUBSCRIPTION'
 		| 'USER_PREMIUM_GUILD_SUBSCRIPTION_TIER_1'
 		| 'USER_PREMIUM_GUILD_SUBSCRIPTION_TIER_2'
-		| 'USER_PREMIUM_GUILD_SUBSCRIPTION_TIER_3';
+		| 'USER_PREMIUM_GUILD_SUBSCRIPTION_TIER_3'
+		| 'CHANNEL_FOLLOW_ADD';
 
 	interface OverwriteData {
 		allow?: PermissionResolvable;
@@ -2611,5 +2641,12 @@ declare module 'discord.js' {
 	type CloseEvent = { wasClean: boolean; code: number; reason: string; target: WebSocket; };
 	type ErrorEvent = { error: any, message: string, type: string, target: WebSocket; };
 
+	interface CrosspostedChannel {
+		channelID: Snowflake;
+		guildID: Snowflake;
+		type: keyof typeof ChannelType;
+		name: string;
+	}
+
 //#endregion
 }