Commander Damage Stacking & Player Control

Question

In Commander/EDH, as far as I understand if a commander does 21 damage to an opponent they lose. I understand separate commanders must be tracked separately in multiplayer.

How does this count if for instance you attack and hit Opponent A, with an 11/11 Commander. Then Opponent B gains control of that same commander (Donate, Confiscate, etc) and on his combat attacks and hits. Is the damage totalled and Opp A loses, or is it tracked separately again? If it’s the latter does commander damage from two different commanders but controlled by the same player stack?

Please include if there are “Mind Control” effects that would yield difference results to this questions.

Answer 1

They would not track separately; the player will lose.

903.10a A player that’s been dealt 21 or more combat damage by the same commander over the course of the game loses the game. (This is a state-based action. See rule 704.)

And

903.3. Each deck has a legendary creature card designated as its commander. This designation is not a characteristic of the object represented by the card; rather, it is an attribute of the card itself. The card retains this designation even when it changes zones.

Basically, no matter who controls a commander, it is still the commander of the deck it started in; it is the same actual commander. While you can take control of a player's commander, there is no way to change it into your commander.

In regards to your question about 1 player controlling 2 separate commanders, this can easily happen with the Partner ability, that allows you to have 2 Commanders. In this case, damage from each commander is tracked separately; you need 21 damage from the same commander to lose the game.

702.123d Except for determining the color identity of your commander, the two commanders function independently. When casting a commander with partner, ignore how many times your other commander has been cast. When determining whether a player has been dealt 21 or more combat damage by the same commander, consider damage from each of your two commanders separately. See rule 903.11a.