Ludevic, Necro-Alchemist

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.

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.

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.