Chainer's Torment

In a Two-Headed Giant game, the first chapter abilities of Chainer's Torment each cause the opposing team to lose 4 life and you to gain 2 life.

As a Saga enters the battlefield, its controller puts a lore counter on it. As your precombat main phase begins (immediately after your draw step), you put another lore counter on each Saga you control. Putting a lore counter on a Saga in either of these ways doesn't use the stack.

Once the number of lore counters on a Saga is greater than or equal to the greatest number among its chapter abilities—in the Dominaria set, this is always three—the Saga's controller sacrifices it as soon as its chapter ability has left the stack, most likely by resolving or being countered. This state-based action doesn't use the stack.

If multiple chapter abilities trigger at the same time, their controller puts them on the stack in any order. If any of them require targets, those targets are chosen as you put the abilities on the stack, before any of those abilities resolve.

If another effect causes the Nightmare Horror token's power or toughness to be a number other than X immediately after it enters the battlefield, the amount of damage it deals to you is still X, not its modified power or toughness.

If counters are removed from a Saga, the appropriate chapter abilities will trigger again when the Saga receives lore counters. Removing lore counters won't cause a previous chapter ability to trigger.