I was alway under the impression that the moment a players health hit 0, all spell effects and permanents under that players control are exiled and that player dies. Is that incorrect?
Scenario:
Defending player has 2 health. Defending player has Gladehart Cavalry on the battlefield. Defending player also has a creature with a 1/1 counter on it.
Attacking player declares attackers, Defending player declares creature with 1/1 counter as blocker.
Trample damage from attacking creature is enough to lower Defending players health to 0 (2 points go through) and kill blocking creature.
Does Defending player gain the 2 life when blocker dies?
I know there's not a ton of card detail. I hope this is enough. If possible, please site sources.
In this scenario, if the attacking creature deals enough damage to the defending player to bring their life total (not: health) to 0 or less, Gladehart Cavalry's second ability will trigger (C.R. 603.2), but that player will lose the game due to state-based actions (C.R. 704.5a) before that ability can even go on the stack (C.R. 116.5; C.R. 510.3, especially C.R. 510.3a, applies here after combat damage is dealt), let alone get to resolve. (See also this thread.) If this is a two-player game, the other player wins and the game ends immediately (C.R. 104.5, 104.2a, 104.1). However, in a multiplayer game, the defending player leaves the game, which means, among other things, that all objects that player owns leave the game and effects giving that player control of any objects end (C.R. 104.5, 800.4a; see also C.R. 800.4d, under which the Gladehart Cavalry ability in this scenario won't go on the stack assuming the defending player controlled Gladehart Cavalry [C.R. 113.8]).
EDIT (Mar. 14, 2020): Add assumption for correctness.
A player does not lose immediately when hitting 0 or less life. But he will lose before any spell or activated or triggered abilty can gain him life back. Losing for having 0 or less life is a state based action, and those are always checked right before any player would receive priority. In the case of combat damage, since that is part of a turn based action, the player loses right afterwards with the next check of SBAs. Lifelink can make a player gain life in time as that is part of the damage results. There are also spells and abilities that can make a player go to 0 or less life and back up all during their resolution, so while the player's life total drops to 0 or less for a brief time, he doesn't lose if he has a positive life total with the next check of SBAs right after the spell/ability has finished resolving.
In your example, the player loses before gaining life. In fact he loses before the trigger can even make it to the stack, because SBAs are checked before triggers go on the stack.
I was alway under the impression that the moment a players health hit 0, all spell effects and permanents under that players control are exiled and that player dies. Is that incorrect?
Scenario:
Defending player has 2 health. Defending player has Gladehart Cavalry on the battlefield. Defending player also has a creature with a 1/1 counter on it.
Attacking player declares attackers, Defending player declares creature with 1/1 counter as blocker.
Trample damage from attacking creature is enough to lower Defending players health to 0 (2 points go through) and kill blocking creature.
Does Defending player gain the 2 life when blocker dies?
I know there's not a ton of card detail. I hope this is enough. If possible, please site sources.
EDIT (Mar. 14, 2020): Add assumption for correctness.
In your example, the player loses before gaining life. In fact he loses before the trigger can even make it to the stack, because SBAs are checked before triggers go on the stack.
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