Yes I did the SFX and Music myself! (I try to learn how to compose and messed around in BeepBox 5h before submitting my game haha).
I thought about changing zombies but I didn't know how to make this feature work and not be annoying when you have to navigate between +40 zombies before getting the right one ^^" also I didn't have much time but after the jam I may revisit this game and implement new mechanics and stages so I'm probably gonna try to implement this idea!