"How does one become a self-taught genius? Naturally, it requires brains."

Ludevic, Necro-Alchemist

At the beginning of each player's end step, that player may draw a card if a player other than you lost life this turn.
Partner (You can have two commanders if both have partner.)

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

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.

Damage dealt to a player causes that player to lose that much life.

If a player lost life and subsequently lost the game, the player whose turn it is may draw a card.

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 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 Falthis and Kediss are your commanders, your deck may contain cards with black and/or red in their color identity, but not cards with green, white, or blue.

Ludevic's ability checks only if another player lost life during the turn, not whether that player's life total decreased over the course of the turn. For example, if a player other than Ludevic's controller lost 2 life and then gained 8 life this turn, the player whose turn it is may draw a card.

Ludevic's ability looks at the entire turn to determine whether the player may draw a card or not. It doesn't matter whether Ludevic was on the battlefield when the opponent lost life.

Ludevic's triggered ability triggers at the beginning of each player's end step, including yours, even if no player has lost life that turn. Whether or not a player has lost life is checked only as the triggered ability resolves.

Ludevic's triggered ability will allow the player to draw a card if any player other than Ludevic's controller, including the player whose turn it is, lost life this turn.

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 any one of them, not from both of them combined.

Only one card may be drawn no matter how much life was lost or how many players lost life.

To have two commanders, both must have the partner ability as the game begins. Losing the ability during the game doesn't cause either to cease to be your commander.

You can choose two commanders with partner that are the same color or colors. In Commander Draft, you can even choose two of the same commander with partner if you drafted them. If you do this, make sure you keep the number of times you've cast each from the command zone clear for "commander tax" purposes.