3 "Artmage" monsters Must first be either Fusion Summoned, or Special Summoned (from your Extra Deck) in Defense Position by Tributing 3 monsters with different Types. You can only Special Summon "Nerva the Power Patron of Creation(s)" once per turn. While a card is in the Field Zone, this card cannot be destroyed by card effects. Once per turn, when you activate an "Artmage" monster's effect (Quick Effect): You can make the activated effect become "Destroy all cards your opponent controls".
