This game is amazing! After almost a month, I finally beat all of the challenges! Here are some tips:
There's only one enemy with 10 health, and it always spawns in one of the corners. When you defeat it, replaces all of the bombs with piles of gold worth 3 XP.
There are only five slimes with 8 health, and they're always on an edge, surrounding an enemy with 1 health. When you defeat that enemy, it reveals where all of the slimes are.
Make sure you use as much of your health as you can before you level up or heal.