Sky Guardian Supreme Dragon, Impede Dragon

(Usable when both fighters' vanguards are grade 3 or greater, and the number of face up G guardians in your G zone is three or less)-Opponent Turn's Guard Step-[Choose a card with "[Heal] Heal" from your hand, and discard it] Call this card to your from face down. :[Choose a face down G guardian from your G zone, and turn it face up] When this unit is placed on , you may pay the cost. If you do, your opponent chooses one of his or her rear-guards, retires it, binds it face up, and if the number of your rear-guards is less than your opponent's rear-guards by two or more, your opponent chooses one of his or her rear-guards, and retires it.