So, recently I've been trying to get past the Totem Kommo-o in Ultra Moon. Now my strategy has kind of varied with each failed attempt, but it starts with my Mr. Mime using Shattered Psyche. Now, since Mr. Mime is part Fairy, the Kommo-o will always lead with Poison Jab, and that's where things get odd.
My Mr. Mime has 101 hp, and after Kommo-o uses Poison Jab, I've seen it left with 1 hp, 2 hp, 4 hp, 6 hp, or it just gets OHKOed. I've saved right before I battle Kommo-o, neither of us get any additional stat boosts or anything (besides all of Kommo-o's stats increasing by 1 but that happens every time so it's a given), and this is always on my first turn, so there's no way the damage output could have been modified at all, so why hasn't it stayed constant throughout all my attempts to beat the Totem? What's with these miniscule hp fluctuations?
As a side note, this isn't the only time I've observed this effect happening, but this was the most recent example and the only one I can remember, so I'm using it for my question.