Brilliant Fusion (Quarter Century Secret Rare)

When this card is activated: Fusion Summon 1 "Gem-Knight" Fusion Monster from your Extra Deck, using monsters from your Deck as Fusion Material, but change its ATK/DEF to 0. If this card leaves the field, destroy that monster. Once per turn: You can discard 1 Spell; the monster Special Summoned by this card's effect gains ATK/DEF equal to its original ATK/DEF, until the end of your opponent's turn. You can only activate 1 "Brilliant Fusion" per turn.