Thanks for the feedback!
Yeah I'll be honest I completely overlooked playtesting in this jam and ended up not knowing exactly how to balance the difficulty, I'll definitely try to pay more attention to that next time and actually get people to test it out first. And thanks for the suggestions! I did actually use VisibilityNotifier2D but it was for the opposite purpose: making them stay on screen most of the time. I made bounds for them though so that they'd be limited only to certain areas of the map, but maybe it could have used smaller sections in the beginning for a smoother difficulty ramp.