Does anyone know what the hidden achievement is? I've scoured the internet for an hour and there is almost no info on this anywhere.

I started this after looking up what Pendleton Ward was up to and seeing he made it. Folks, it's awful. I haven't been shy in my dislike of rogue-lik/tes, but this is truly bad. It's barely anything. It's a RNG with Adventure Time graphics. It doesn't even feel good to clear a level, because there is no skill involved, just luck of the draw. It's even worse than card-based roguelites like Slay the Spire and Solitairica, those at least offer a bit more choice and strategy in a build. I have 24 of the titular cards and can use up to five at a time. I'm using two cards to boost my chance not to get hurt, two to boost my max HP (by a total of 3...) and the last one adds another potion to each floor. Practically, this doesn't help me much at all. Just not very fun dying because you have no choice over and over and over and over and over again.