Nervedo the Shadebeast Power Patron

(This card is always treated as an "Artmage" card.)
You can banish the top 3 cards of your Deck face-down; destroy this card, and if you do, Special Summon 1 "Nerva the Power Patron of Creation" from your Extra Deck (this is treated as a Fusion Summon). If this card is added to your Extra Deck face-up: You can Special Summon 1 "Power Patron" or "Artmage" monster from your Deck or face-up Extra Deck, except "Nervedo the Shadebeast Power Patron". You can only use each effect of "Nervedo the Shadebeast Power Patron" once per turn.