The enemy player can't play spells for the next three turns.
Onslaught: For each attack you or your units made this turn, give that much Strength and Health to that many units on your deck.
Card sounds may differ from in-game as they get updated.
Onslaught - Does something when played if you or any of your units have attacked this turn. This includes standard attacks as well as Killer and Relic Weapon attacks.