Duel Commander follows the exact same rules as classic multiplayer Commander, except for the following.
First, players start the game with 30 life.
Also, the following cards are banned :
- Ancestral Recall
- Ancient Tomb
- Balance
- Back to Basics
- Black Lotus
- Channel
- Crucible of Worlds
- Gifts Ungiven
- Grindstone
- Hermit Druid
- Humility
- Imperial Seal
- Karakas
- Library of Alexandria
- Mana Crypt
- Mana Drain
- Mana Vault
- Mind Twist
- Mishra’s Workshop
- Mox Emerald
- Mox Jet
- Mox Pearl
- Mox Ruby
- Mox Sapphire
- Necropotence
- Sensei’s Divining Top
- Serra Ascendant
- Shahrazad
- Sol Ring
- Strip Mine
- The Tabernacle at the Pendrell Vale
- Time Vault
- Time Walk
- Tinker
- Tolarian Academy
- Vampiric Tutor
- Vanishing
- Yawgmoth’s Bargain
Ante cards and manual dexterity cards are also banned.
The following cards are also banned from being played as a commander :
- Braids, Cabal Minion
- Edric, Spymaster of Trest
- Erayo, Soratami Ascendant
- Rofellos, Llanowar Emissary
Also, the legends rule doesn’t apply to commanders as long as both creatures with the same name on the battlefield are commanders. If a creature with the same name is on the battlefield but is not a commander (either because it is played as a “normal” creature or because of a card like Clone), the legend rule applies and all those creatures are put into their owners’ graveyards as the result of a state-based effect.
Finally, in addition to the ability to put the Commander back into the Command Zone if it would go to the graveyard or be exiled, you may do so also if it would be put into your library.
Why specific rules for Duel Commander ?
When you play a game with more than two players, social interactions, diplomacy and negotiations usually prevent a player from taking a huge advantage at the start of the game. Indeed, if a players becomes the main threat at the table, it is likely that he will become the top priority target for other players. Such a player should have to face several opponents at the same time, which brings balance in the game. Multiplayer games tend to be balanced by diplomacy.
When only two players are facing each other, this cannot be done. If a player takes a great advantage early in the game (example : turn one Island, Lotus Petal, Mana Crypt, Jace the Mind Sculptor), his opponent won’t be able to get back in the game. That is why we banned certain cards which lead to extraordinary early game advantages from which an opponent cannot recover (Mana Crypt, Sol Ring…). Some cards are banned as commanders for this purpose : those cards can still be played in your deck, but can’t be chosen as a commander. We also removed certain cards which can easily lead to degenerated combos, such as Hermit Druid.
Sometimes a tournament is organized for Duel Commander. Such events need to put a time limit in rounds, generally between 50 and 60 minutes per round. Considering the time restrictions, we banned Sensei’s Divining Top and Shahrazad, because they tend to make games last considerably longer, leading to numerous unfinished games at the end of the round.
Apart from the points mentioned above, all the rules of Duel Commander obey the rules of classic multiplayer Commander.
You can find more complete explanations in the Duel Commander Rules Summary.