This is an old topic, so hope you don't mind my revisiting it...
The stamina stat may not be necessary and could just be annoying. The player's own stamina will come into play anyway, as multi-hit moles will require them to tap the screen a _lot_!
You could cut down on the tapping, introduce more variety and make the game more like an RPG by introducing puzzle elements. For example, moles that you have to tap in sequence or your blows do nothing. Or swipe the screen to remove the spiked hats from enemies before bopping them. Pin smart bombs could pop the bubblegum mole's bubbles so you can dispatch them safely. You could also feature a wider variety of weapons such as charged hammers that build up force for their next hit while you are not tapping the screen (good for small numbers of powerful moles) or wide mallets that do little damage but hit multiple holes at the same time (great for whacking lots of weak enemies).
Your background story sounds super creepy! Could be an interesting black humour direction, a bit like Binding Of Isaac. I don't know if you might be overly limiting your audience with that.
wow! very neat ideas, thanks!