Resurgam XYZ

All Xyz Monsters you control gain 800 ATK. Once per turn: You can discard 1 Spell, then target 1 Xyz Monster you control; Special Summon from your Extra Deck, 1 "Number C" monster or 1 "CXyz" monster, with the same Type as that monster you control but 1 Rank higher, by using it as material. (This is treated as an Xyz Summon. Transfer its materials to the Summoned monster.) If you discarded a card other than a "Rank-Up-Magic" Spell to activate this effect, return that Special Summoned monster to the Extra Deck during the End Phase (even if this card leaves the field).