Sivriss, Nightmare Speaker

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.

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.

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

You can choose two commanders that are the same color or colors.

To resolve the activated ability, first mill a card for the first opponent in turn order. That player chooses whether to pay 3 life or not. The card is returned to your hand unless they paid the life. Then mill a card for the next opponent, and so on.

If Sivriss somehow becomes an artifact, you may sacrifice it to its own ability.

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).

If a card refers to a commander creature you own, a Background won't usually be counted or included for that effect. If another spell or ability causes your Background to become a creature, however, it will be included. Any effect that refers to your commander or a commander you own or control without specifying creature will apply to a Background that is your commander, as appropriate.