Mastery 6: Put an 8/8 Sword of the Sky King into your deck.
Card sounds may differ from in-game as they get updated.
Warcry - Each time a unit or Relic Weapon with Warcry attacks, it grants a permanent bonus to the top-most unit or weapon in your deck. Even if it's a few cards down, you'll get to stack up the bonuses on it over multiple turns.
Mastery - All damage dealt by units with Mastery count towards its Mastery ability. When its Mastery number is met, it uses its Mastery ability.