Seems like a lot of people are talking about AI so lemme chime in.
As someone who's dabbled with AI extensively. Looking at the game, I personally don't see any AI Images being used nor clear indicators or fractals of it... so far. More likely scenario for me at least is that nitrolith just improved at drawing over the years of making this game. Reminds me of how bad Weirdworld(creator of superhuman)'s art was at the start but got wayyy better. Of course, some said it was AI but in reality they just got better at drawing but yk, they're still human so they can occasionally fuck up with some anatomy here and there. I'm guessing it's the same case for hero party must fall.
However, for those still insistent that it is AI, my best guess is that they either used all of their drawings from the past and used it as the basis of the art generation for the ai. TLDR for those who dont get that: they just trained the ai to learn their art style. Alternatively, nitrolith could have used ai art then draw over it hence explaining those weird things people have said before me.
Still, I don't think any AI was used.... emphasis on so far.
Regardless, ya'll still gonna play this game either way and nut non stop XD