- Vampires spawning (not with bats) naturally are basically a game-ender. I think that their damage should be limited to 1 heart (total) whenever some of them are concentrating.
- When you pick up an item with a full inventory there should be a way to decline throwing one away (i.e. a back button), like you have with the keys. This might already be in but I couldn't find out how to do it.
- Heroes being lost isn't really a fun mechanic, especially when they don't offer much advantage over the starter character, if any. If they're going to be lost maybe they should actually accompany the starting hero in some way (i.e. only in the dungeon where you free them), else a permanent unlock system of some sort would probably be better.