BoastBoast is a keyword that adds additional rules to the activated ability that follows it. “Boast — [Cost]: [Effect]” means “[Cost]: [Effect]. Activate only if this creature attacked this turn and only once each turn.”
Effects may refer to boast abilities. If an effect refers to a creature boasting, it means its boast ability being activated. (CR 702.142) —
: Return target creature card from your graveyard to your hand. (
ActivateTo activate an activated ability is to put it onto the stack and pay its costs, so that it will eventually resolve and have its effect. Only an object’s controller (or its owner, if it doesn’t have a controller) can activate its activated ability unless the object specifically says otherwise. A player may activate an ability if they have priority. See rule 602, “Activating Activated Abilities.” (CR 701.2) only if this creature attacked this turn and only once each turn.)