I keep fighting the same boss over and over again until I get good enough to beat them, but why don't they get better at beating me at the same time?

It'd be a shitty game experience but it'd be unique if a boss adapted to your style at the same time as you adapted to theirs.

@danlew I vaguely remember some short indie game where it remembers the actions you take against an enemy, and then uses your actions as the script for the next round of the enemy, repeat until fall

@gray17 Perhaps Warning Forever (https://en.wikipedia.org/wiki/Warning_Forever)?

That's really close to what I am thinking about, but it's not style adaptation so much as "boss gets adaptively beefier each time."

Warning Forever - Wikipedia

@danlew found this game, which is not the one I was thinking of, but has a similar idea
https://store.steampowered.com/app/2875510/RAD_Repeat_After_Death/
Steam:RAD: Repeat After Death

The task is simple, defeat enemies using various Characters. But, your past move will consume you the more you continue down the path. Discover the dungeon mysteries while engaging with the other dungeon dwellers