Wind-Up Zenmaister (Starfoil)

2 Level 4 monsters // This cards gains 300 ATK for each of its Xyz Materials. Once per turn, you can detach 1 Xyz Material from this card to select 1 face-up monster on the field that you control. Flip that monster into face-down Defense Position. During the End Phase, the selected monster is flipped into face-up Attack Position.