If a monster(s) is Special Summoned to your field face-up (except during the Damage Step): You can target 1 of them; Special Summon this card from your hand, and if you do, change that monster to face-down Defense Position. If this card is sent from the hand or field to the GY: You can target 1 monster on the field; change it to face-up Attack Position or face-down Defense Position. You can only use each effect of "Green Ninja" once per turn.