Hardest fight

Obviously Ultra Necrozma and Totem Lurantis. Difficult to think of another one, possibly Team Rainbow Rocket bosses.

Oh, well, I forgot to mention one more thing in USUM that I found to be a pain in the neck: Totem Ribombee. I know that it's supposed to be a breather battle after Ultra Necrozma and before Hapu, but how if this thing comes with +2 to all stats, Quiver Dance + Draining Kiss, and a possible partner with Heal Pulse and Light Screen? Mean. At least Toxic stalling worked wonder in my case.

Ultra Necrozma but that's a no-brainer.

Totem Togedemaru can also screw itself. I had nothing good for this thing and it was so damn strong.

Yeah, Ultra Necrozma. It had too high a level and boosts, so it felt a bit cheap, but it was the hardest, for better or worse.

Ultra Necrozma hands down prob the hardest battle I've ever had, thank god for toxic