Game modes

Game modes are a set of restrictions, or lack of, within which the game of Dota 2 can be played. Some game modes are exclusive to Matchmaking, whereas other - more novelty - game modes are restricted to use within private lobbies.

All Pick
The entire hero pool is available for players to choose from; heroes are removed from the pool when they are chosen. Players can choose any hero, pick a hero at random, re-pick a hero, or swap heroes with teammates once in-game before the game begins. There are gold costs associated with picking or re-picking heroes, though random is free.

Single Draft
Each player is given a pool of three heroes to choose from; each hero being a random choice for each attribute - strength, agility, intelligence. Players can choose from one of those three heroes, re-pick a hero; but players can not random, nor can they swap heroes with their teammates.

Captain's Mode
Almost the entire hero pool is available for captains (the first player in each team) to choose from; captains go through an order of picking & banning to choose their team's hero pool and remove heroes from the pool available - picking 5 heroes for their team by the end. Once each team's 5 heroes have been chosen, players can then choose which of those 5 heroes they wish to play.

As of the current version Centaur Warrunner, Huskar, Medusa, Troll Warlord, Elder Titan, and Abaddon are unavailable in Captain's Mode.

The most recent patch of the wc3 mod (6.78) has Huskar, Phoenix, Earth Spirit, Abyssal Underlord, Medusa, Arc Warden, Oracle, and Winter Wyvern unavailable in Captain's Mode. This implies that when implemented in Dota 2, Legion Commander, Ember Spirit, Soul Keeper, and Goblin Techies will be available in Captain's Mode.

Captain's Mode is typically the standard format for tournament games.

The pick and ban order for Captain's Mode is (Team 1 = green, Team 2 = red): BAN -> BAN -> BAN -> BAN -> PICK -> PICK -> PICK -> PICK -> BAN -> BAN -> BAN -> BAN -> PICK -> PICK -> PICK -> PICK -> BAN -> BAN -> PICK -> PICK

Random Draft
A limited hero pool of 22 heroes is available for players to choose, however players cannot choose their hero straight away - the game alternates between players allowing them their slot to choose a hero.

The order of choosing heroes in Random Draft is: Radiant #1 PICK -> Dire #1, #2 PICK -> Radiant #2, #3 PICK -> Dire #3, #4 PICK -> Radiant #4, #5 PICK -> Dire #5 PICK.

Least Played
You have a limited pool of heroes in which to choose from; the pool excludes your 40 most played heroes. Players can choose any hero from that pool, pick a hero at random, re-pick a hero. There are gold costs associated with picking or re-picking heroes, though random is free.

Limited Heroes
Identical to All Pick, except you may only choose from a subset of the hero pool (selected from the easier to play heroes; the mode is aimed at easing beginners into the game). Heroes playable in the limited pool are:

Bounty Hunter, Death Prophet, Dragon Knight, Drow Ranger, Juggernaut, Lich, Lion, Omniknight, Razor, Sand King, Skeleton King, Sniper, Sven, Tidehunter, Vengeful Spirit, Viper, Warlock, Windrunner, Witch Doctor, Zeus

All Random
All players are assigned a random hero.

Reverse Draft
Like Captain's Mode, but Radiant's captain picks the heroes for the Dire and vice versa. This is currently only available in private lobbies.

Mid Only
Lane creeps only spawn in the middle lane, and players can pick the same heroes. This is currently only available in private lobbies.(Note: in the current version, avoid picking multiple meepos,shadow fiends,wisps. Rubick and Bane are also buggy.)

Quests
Quests are short scripted scenarios focused on teaching new players the mechanics of the game, or in more advanced ones, put them to test.