Livaan, Cultist of Tiamat

Once the game begins, your two commanders are tracked separately. If you cast one, you won’t have to pay an additional {2} the first time you cast the other. A player loses the game after having been dealt 21 combat damage from any one of them, not from both of them combined (although your Background won’t usually be a creature anyway).

An effect that checks whether you control your commander is satisfied if you control one or both of your two commanders.

If your Commander deck has two commanders, you can include only cards whose own color identities are also found in your commanders’ combined color identities.

If something refers to your commander while you have two commanders, it refers to one of them of your choice. If you are instructed to perform an action on your commander (e.g. put it from the command zone into your hand due to Command Beacon), you choose one of your commanders at the time the effect happens.

If you control a Background that grants an ability to commander creatures you own, and you own more than one commander creature, each of them will have that ability.

Both commanders start in the command zone, and the remaining 98 cards (or 58 cards in a Commander Draft game) of your deck are shuffled to become your library.