You need something as an anti-poison or clock work heart is killed by poison nearly every time.
Additionally taking clockwork heart seems to not allow you to keep any gains to max hp between rounds, which is very punishing. It also make max hp items virtually useless.
Finally if fighting the big boss and a watermelon spawn in the slot directly down from the boss it is impossible to select the watermelon.
All that being said good game, decently well balanced