Details: After defeating Mina, she will tell you that the Ultra Beast this Time around is Xurkitree, and that there have been two of them spotted in either Lush Jungle or Memorial Hill. She then leaves, and it is up to you to capture both of them. Like all the previous Ultra Beasts, you will know you are close to Xurkitree, an Electric Type Pokemon, in either Lush Jungle or Memorial Hill by the change in background music.
Both Xurkitree will be at Level 65, knowing the Moves of Hypnosis, Discharge, Electric Terrain, and Power Whip. Since it's a pure Electric Type, you cannot paralyze this Ultra Beast. And as like the other Ultra Beasts, Xurkitree will have one of its Stats doubled immediately as the Battle begins. This Stat is none other than its Special Attack Stat, which just so happens will also increase after knocking out each Pokemon on your team since its Beast Boost Ability.
After catching not one, but both Xurkitree, report back to Anabel and Looker on Route 8 to continue the storyline.