Thanks for the detailed feedback!
Sponge being one-time use is very experimental, I'll let it be like that for a while, maybe I'll lower the price
I'll tune down Malfunction, I experienced some struggles against it as well
Might switch Pickpocket and Tourist around in chapter order, and nerf/buff them accordingly
I'll think about switching some enemies around between chapters if you're saying Red is too good in chapter 3. Maybe Spike belongs there
I'll look into the bugs with all the items mentioned