After defeating Ultra Necrozma and returning to The Alola Region, the Ultra Recon Squad will continue to allow you to explore Ultra Space with the help of their Legendary Pokemon. While traveling through Ultra Space, you may sometimes enter a White Wormhole that leads to Ultra Ruin. This is the dwelling place of Guzzlord.
In order to battle Guzzlord, you will have to reach the end of this area, the same that is the ruins of Hau'oli City. Guzzlord remains a Dark / Dragon Type Pokemon, always being found at Level 60 and knowing the moves of Hammer Arm, Thrash, Gastro Acid, and Heavy Slam. Like all other Ultra Beasts, it can now be found in its Shiny Form. It will also respawn with each successive visit to this area.