Fairy Tail - Sleeper (INOV-EN035) - Invasion: Vengeance Unlimited

FLIP: You can Special Summon 1 monster from your hand. During either player's turn, when your opponent activates a Normal Spell/Trap Card: You can Tribute 1 other monster; the activated effect becomes "Change 1 face-up monster your opponent controls to face-down Defense Position". You can only use this effect of "Fairy Tail - Sleeper" once per turn.