Major bug: if you play normal mode after cruel mode, normal mode has permadeath. I was really confused because I tried hard mode first, and I thought maybe you had your own definitions of words like "permadeath" and "respawn."
Other bugs: one time I was fighting the hero in normal mode and his health bar didn't appear. Also, it looks like the cruel heart doesn't count as picking up an item in terms of the description showing up and the ending screen showing how many items you got.
I'm curious to know the likelihood of the cruel heart appearing. Some runs I don't get it at all, but one time I saw it spawned by three bosses in a row.
It would be cool if keeping the flower until the end had some effect on the ending.
I can see that a lot of people are unhappy with the core mechanic, but real gamers like me aren't going to complain about a special challenge like this. As your author comment implies, the idea is to give you a potential reason to shoot less often. You have to decide how many blades you want on the screen at once, and that's a fine game idea. It would feel more fair if your enemies could also harm themselves, but I guess maybe the unfairness goes with the premise of playing as the villain. It's meant to reverse game tropes and expectations.