Xyz Universe [RA04-EN218] Quarter Century Secret Rare

Target 2 face-up Xyz Monsters on the field; send both monsters to the GY, then Special Summon 1 Xyz Monster from your Extra Deck, except a "Number" monster, whose Rank is equal to, or 1 less than, the combined original Ranks of those 2 Xyz Monsters, and if you do, attach this card to it as material, also, for the rest of this turn after this card resolves, your opponent takes no damage.