Since this was one of the very few games that was completed this marathon, and it was also a short game, I decided to make a highlight of the whole playthrough. I would say it's a speedrun, but it really isn't. Anyway, enjoy!
Title pretty much sums it up. I made it to the crab boss on level 5. The first time, he was actually there, but I died and had to continue, having to do all of level 5 again. When I made it back to the boss room this time around...he wasn't there! Fortunately, leaving the top-down area and re-entering fixed it.
I discovered this when I was doing a practice speedrun on Rising Mode. I have been able to do this a couple times, but I'm not certain what causes it or what significance it has if any. It is neat though!
btw, this occurs at the beginning of level 3.
This is, in my opinion, the hardest floor in Bloody Palace. I say that because you have to fight two Blitzes at the same time, they dish out DMD difficulty damage, and if you don't take them out fast enough, they can activate Devil Trigger, which makes them even stronger. Just follow what I do in the video and you should be able to take them out no problem.