Crystal Keeper (Common)

Pendulum EffectEach turn, the first an Ultimate Crystal monster(s) and/or Crystal Beast card(s) you control that would be destroyed by a card effect that turn, it is not destroyed.Monster EffectIf a Crystal Beast monster you control battles an opponent's monster, during damage calculation (Quick Effect): You can Tribute this card from your hand or face-up from your field; your battling monster's ATK/DEF become double its original ATK/DEF during that damage calculation only, but it is destroyed at the end of this Damage Step.