It's a lot of fun! I played for half an hour and it was incredible! A bit confusing with some bonuses, I was accumulating hearts right before the boss battle and I had no damage, I died quickly despite those hearts =)
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I'm really sorry, I did a poor job of conveying this information to the players. Upgrading Heart and obtaining mutations for heart both increase the maximum health value (and they multiply together). I didn't clearly communicate this mechanism, and it's such a shame that you lost your game for that. My bad!