Since Poipole is the first Ultra Beast you will obtain and since it can evolve, the second Ultra Beast you are likely to obtain is Naganadel, none other than the very evolution of Poipole itself. In order to evolve Poipole into Naganadel, Poipole must level up while knowing the move Dragon Pulse. Naganadel will be a Poison / Dragon Type Pokemon, being a very fast special attack sweeper.