So I was all set to come back here after finishing White Castle to say that actually, the hack turned out to be alright in the end, but the final level (the titular Castle) is miserable. Not only is it a massive difficulty spike, but it has a design choice so bafflingly terrible that I cannot possibly imagine what the creator was thinking when they decided to put it in: the rooms have multiple checkpoints in them, but when you die, you go back to the checkpoint before the last one you got. So for example if you die after getting the third checkpoint, you restart at the second one. Then if you die before reaching the third checkpoint again, you restart at the beginning of the room. It's unnecessarily punitive, and massively disrespectful of the player's time.
After two hours I made it through three long rooms and a boss fight, and fully expected to be rolling credits, but I ended up in another room. At this point it was past midnight so I decided to look up how much was left, and boy was I surprised: there were two more rooms, another boss, a cape room, and then a third boss. All of them are long, just as difficult, and have that shitty checkpoint system. So yeah, I'm done with this one. Mario and Luigi will just have to go hungry tonight.