Muzurhythm the String Djinn [SP14-EN028] Starfoil Rare

2 Level 3 monsters When a "Djinn" Xyz Monster you control is attacking an opponent's monster, during the Damage Step: You can detach 1 Xyz Material from this card; the attacking monster's ATK is doubled until the End Phase. You can only use the effect of "Muzurhythm the String Djinn" once per turn.