Boast

Boast is a keyword ability introduced in Kaldheim.

Description
Boast keyword adds a drawback to an activated ability which is referred as the boast ability. The drawback is as follows: a player can only activate the boast ability after the creature with the ability attacks and at most once each turn. Boast abilities can be activated during combat or even after combat — any time in the turn after the creature was declared as an attacker.

Cards interacting with Boast

 * Birgi, God of Storytelling allows a second Boast ability activation.
 * Dragonkin Berserker reduces Boast abilities by for each Dragon you control.

Rulings

 * A boast ability can be activated at any point after the creature with that ability has been declared as an attacker. This can be before blockers are declared, after blockers are declared but before combat damage is dealt, during combat after combat damage is dealt, during the postcombat main phase, during the end step, or, in some unusual cases, during the cleanup step.
 * If it's not your turn and you gain control of a creature with a boast ability after that creature attacked, you can activate that creature's boast ability if it hasn't been activated yet that turn.
 * If a creature with a boast ability is put onto the battlefield attacking, it was never declared as an attacker. Its boast ability can't be activated that turn.
 * If an effect adds additional combat phases to a turn and a creature with a boast ability attacks more than once during that turn, its boast ability can still be activated only once.