Ah, I see, guess I didn’t get further then 4 levels, then. The major problem is that when you rewind, both the enemy and the yellow bullet travel backwards in time exactly to the point when the enemy shot the bullet. Still it gets challenging with many enemies, so this isn’t a big problem, of course.
Viewing post in Rewind Bullethell jam comments
Yes, indeed that is a problem that I didn't quite nail, I didn't initially design it like that tbh; initially the enemies didn't rewind, only the bullets. But I found what was happening was the bullets would go back to their origin and most often not hit an enemy (because the enemies move up and down slightly too, if the bullet spawned at the front they de-materialised before they could even reach an enemy). I thought it would be quite frustrating for the player to wait for the rewind to unlock only to then miss a bunch of enemies, I found it was more enjoyable hitting the rewind button, having to dodge bullets in both directions, but then be paid off by destroying a bunch of enemies.
I wish I had started the game a few days earlier, I wouldn't have had the respawn bug and I could have made the difficulty curve a bit better.
Thanks again for the extra feedback :)