Okaun, Eye of Chaos

If an effect has a player flip a coin and refers to winning or losing a flip, only the player who flipped the coin wins or loses the flip. If that player loses the flip, nobody wins the flip.

The triggered ability of the “partner with” keyword still triggers in a Commander game. If your other commander has somehow ended up in your library, you can find it. You can also target another player who might have that card in their library.

“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.”

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.

If a creature’s power is less than 0 when it’s doubled, instead that creature gets -X/-0, where X is how much less than 0 its power is. The same is true for its toughness. For example, if an effect has given Okaun -7/-0 so that its power and toughness are -4/3, doubling its power and toughness gives it -4/+3 and it’s -8/6 until end of turn.

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.