Naglfar, Generaider Boss of Fire

You can only control 1 "Naglfar, Generaider Boss of Fire". If a card(s) you control would be destroyed by battle or card effect, you can destroy 1 "Generaider" monster or 1 Beast-Warrior monster you control instead. You can only use this effect of "Naglfar, Generaider Boss of Fire" once per turn.