Subterror Nemesis Defender

During either player's turn, when your opponent activates a card or effect that targets exactly 1 Set monster you control (and no other cards), or when a Set monster you control is targeted for an attack by an opponent's monster: You can send this card from your hand or face-up from your field to the Graveyard, then target another monster you control that would be an appropriate target; that card/effect/attack now targets the new target. While you control a Set monster, this card cannot be destroyed by battle or card effects.