Maybe make Schoolbag a guaranteed spawn on like, the second shop or something? Without it, runs get a lil boring, but with it, it's too powerful early on. Some way to theoretically be able to get it would be really nice. Also, add Robo-Baby! Slow firing, basic damage piercing beam for 200 hearts. One isn't enough to take out an entire enemy on its own, but it hits everything in the row (it it can). Also, you could have Robo-Baby 2.0 in the shop as a phantom Robo-Baby behind your other babies that can be moved up and down minecart style.