Mastery 1: Play a +1/+2 weapon on Akko.
Mastery 9: Units and weapons in your deck get +4/+2 and Overwhelm.
Card sounds may differ from in-game as they get updated.
Overwhelm - A unit or spell with Overwhelm will deal any excess damage to your opponent on your turn (does not work while blocking).
Mastery - All damage dealt by units with Mastery count towards its Mastery ability. When its Mastery number is met, it uses its Mastery ability.