5 minutes for one point of stamina regen is a little bit too long if most actions that need them took more than 5 points. Cracking the puzzle would take more than 40 points later on. :/
Nice graphics, cute drawing and good music. Sad that it's still rather unbalanced, at least nerf the dragon more and gave us more income. Or at the very least, make that level up affect the rate the lifespan decrease or the health amount. I don't care about the score multiplier, this would have made a somewhat good idle game.
I think there's a bug whenever your enemy casted regeneration. It would never run out of effect and therefore would make boss battle unnecessarily harder and longer.
Ok, then you need to find a way to have a look at the book... maybe you can distract the delivery boy somehow..!