Life gain that happens to either head affects the shared life total.

Do triggered abilities (on an object controlled by one head) that look for a player to gain life trigger based on life gained only by that head?

810.9. Damage, loss of life, and gaining life happen to each player individually. The result is applied to
the team’s shared life total.

Does the trigger look at the resulting game state change or the actions contained within the event to determine if it triggers?

edit: the more I think about it, I think it's the actions within the event that can be carried out (ie. aren't impossible) that determine the trigger

Edited Todd Bussey (Feb. 21, 2013 09:26:26 PM)

I'm assuming that you are asking about cards such as Ajani's Pridemate, which ask for a specific player gaining life. If we take the literal words from 810.9, then I would rule that Ajani's Pridemate would only trigger if you gained the life specifically. Examples would be if a creature you controlled had lifelink, or if you had cast an Angel's Mercy. Therefore, I don't think that such triggers would happen if your teammate had done either of the above.

Awaiting a senior judge / other opinions to make sure I haven't neglected something.

Would Pridemate trigger if my team exchanged life total with another team that had a greater total?

How about this… Your team is at 1 life and you control a 0/11 tree of redemption. Both you and your partner each control Rhox Faithmender. You activate Tree of Redemption to swap life totals going up to 11. After triggers, does your final life total end up being 21 or 41?

Originally posted by Todd Bussey:

Would Pridemate trigger if my team exchanged life total with another team that had a greater total?

There are no effects that exchange team's life totals. In 2HG, a player can exchange his or her life total with an opponent, which will result in the player's team's life totals being exchanged. For any abilities that care about players gaining or losing life, the exchange happened between two players, not between two teams. In the exchange, one player gained life and one player lost life (if the life totals are different).

So, if your team's life total is lower than your opposing team's life total and you exchange life totals with one of your opponents, your Pridemate would trigger, while your teammate's Pridemate would not trigger.

Rule 810.9 means that the only player who is considered to gain life is the player who is instructed to gain life. So your Ajani's Pridemate doesn't trigger if your teammate is instructed to gain life.

In the Tree of Redemption scenario only your own Rhox applies, so your life will be set to 21. Also, Rhox Faithmender's ability doesn't trigger (it doesn't use the words “when”/“whenever”/“at the beginning”/“at end”). It's a static ability that creates a replacement effect.

Edited Nelson Mendoza Moral (Feb. 21, 2013 11:24:27 PM)

Originally posted by Adam Zakreski:

How about this… Your team is at 1 life and you control a 0/11 tree of redemption. Both you and your partner each control Rhox Faithmender. You activate Tree of Redemption to swap life totals going up to 11. After triggers, does your final life total end up being 21 or 41?

There are no triggers involved here. Rhox Faithmender has a static ability that creates a replacement effect. (The phrasing “If something would happen, something different happens instead” is one of the ways a replacement effect can be worded. Triggered abilities use the words “when,” “whenever,” or “at.”)

Now that that's out of the way, let's recall what the above rule says: Players gain and lose life individually. When you activate the Tree, the exchange would cause you to gain 10 life. The game looks for applicable replacement effects, sees your Rhox Faithmender's effect, and applies it, which doubles the life gain to 20. Your teammate's Faithmender doesn't care about this because it's not your teammate who is gaining life here. The modified event happens and you gain 20 life. This life gain is applied to your team's shared life total, so your team's life total ends up at 21.

I've essentially looked at it as setting a higher life total “counts as life gain”. I guess another way to look at it would be that setting a life total is a short form of saying, “gain X life where X is the difference between their current life total and someNumber.”

That's what the rules say:

118.5. If an effect sets a player’s life total to a specific number, the player gains or loses the necessary amount of life to end up with the new total.

701.8c When life totals are exchanged, each player gains or loses the amount of life necessary to equal the other player’s previous life total. Replacement effects may modify these gains and losses, and triggered abilities may trigger on them.

There we go! I was looking at 701.8g.

Thanks Nelson!