First of all thank you very much for the feedback (my first feedback for this game :D).
1, 2, somewhat 3 and 5 are bugs that I will 100% fix (I think I know the issue).
Regarding 3 in more detail: I was planning to do a "Your stats screen" which would show current stats with power ups but decided to wait for feedback.
4 is my choice as for the last boss you would either need to grind a lot or to be skilful in balance of killing normal slimes and damaging the boss
Once again, thank you for the detailed feedback. Everything is noted. Be sure to check out the updated version next week (or this weekend) :D
Much love <3