Comprehensive Rules

Commander Selection

A card’s color identity includes its color plus the color of any mana symbols in the card’s rules text.
Established before the game begins, a card’s color identity cannot be altered by game effects.
The cards in a deck must not feature colors outside the commander’s color identity.

A Commander deck must be exactly 100 cards, including the commander.
If using a companion, it must follow color identity and singleton rules, counting as the 101st card.
Except for basic lands, no two cards may share the same English name, unless allowed by specific card rules.

Players start with 25 life.
Commanders start in the Command Zone and can be cast following normal rules, with an additional 2-Mana cost for each previous casting.
Commanders moving to a library, hand, graveyard, or exile can be redirected to the command zone.
Being a commander is not a characteristic [MTG CR109.3], it is a property of the card and tied directly to the physical card. As such, “commander-ness” cannot be copied or overwritten by continuous effects. The card retains it’s commander-ness through any status changes, and is still a commander even when controlled by another player.
A player may cast a commander they own from the command zone. A commander cast from the command zone costs an additional {2} for each previous time the player has cast a commander from the command zone that game. This additional cost is informally known as the “commander tax.” This is the Centurion commander variant to [MTG CR 903.8]
A player loses if they receive 21 combat damage from a single Commander.
Commanders adhere to the Legend rule; no player can control more than one legend of the same name.
Cards bringing others from outside the game do not function in Commander.