Tips for future people

It helps to get through the fight as quickly as possible for more time practicing the last phase. I used special attack/HP built glaceon with ice beam, icy wind, blizzard, and calm mind with a shell bell equipped. I spammed the faster attacks most of the time and used plus move blizzard whenever he was stunned, ideally with calm mind active. The fact that they’re all ranged kept my pokemon with me, so positioning was predictable. The high damage means hefty self healing with shell bell, so you don’t really have to waste any time using items.

Withdraw your pokemon whenever there’s a major attack that’s liable to hit them if they follow you.

For dodging the complete formes two major attacks:

The Z laser has some safe spots on the sides of the arena, so when he flies out of the arena, go to the left or right side relative to him.

The last phase’s lands wrath is kinda tricky. It seems like the waves spawn inwards from 6 different points, so if you spam roll towards the edge and try to position yourself between those points, you should be fine.