Game was unbearably slow to progress normally, so I eventually fired up Cheat Engine to see what content was there.
When at the lowest resolution, the text is unreadable, and the prestige screen does not have the options menu so I couldn't change resolution until after it was no longer useful.
When one-shotting enemies, there's a shake effect that should be possible to disable. Especially with speed upgrades, the game ends up just constantly shaking.
The first boss joins after being defeated, but the second does not. I assume this is because the game progression ends there, but I'd prefer for the boss to join before the progression ends.