Sylvia Brightspear

“Partner with [name]” represents two abilities. The first is a triggered ability: “When this permanent enters the battlefield, target player may search their library for a card named [name], reveal it, put it into their hand, then shuffle their library.”

If your Commander deck has two commanders, you can only include cards whose own color identities are also found in your commanders’ combined color identities. If Khorvath and Sylvia are your commanders, your deck may contain cards with red and/or white in their color identity, but not blue, black, or green.

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

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 damage from one of them, not from both of them combined. Command Beacon’s effect puts one into your hand from the command zone, not both.

To have two commanders, both must have the partner ability (featured in the Magic: The Gathering—Commander™ (2016 Edition) set) or corresponding “partner with” abilities as the game begins. A creature with a “partner with” ability can’t partner with any creature other than its designated partner. Losing a partner ability during the game doesn’t cause either to cease to be your commander.

Note that the target player searches their library (which may be affected by effects such as that of Stranglehold) and that the card they find is revealed, even though these words aren’t included in the ability’s reminder text.