Saga of the Dragon Emperor

Target 1 Dragon monster you control; double its current ATK (until the end of this turn), then, if your opponent controls a Dragon monster, the targeted monster's effect activations cannot be negated this turn. During your Main Phase: You can banish this card from your GY; Special Summon, in Defense Position, 1 of your Dragon Xyz Monsters that is banished or in the GY. You can only use 1 "Saga of the Dragon Emperor" effect per turn, and only once that turn.