This is amazing concept :) I love it, it has so much potential but why not always deposit all you money at the bank then withdraw it. It is not clear the effect of having mixed coin especially because there is no animation of which coin is head and which one is tails :) maybe this random luck part should not be there or reduced by making the damage happen if at least one coin landed head which give me a reason to add more of the same coin because I have more chance to do more damage and at the same time making the idea of having pennies is good as it will add small damage but will increase the odds of landing a hit.

Great work, let me know if you continue working on it :) I would love to help if you are up to it :)

This is a real clever mechanic, especially how trading-up denominations is a natural and understandable progression arc. Not being able to heal makes it a bit brutal at the hands of the RNG, but really enjoyed playing.