Spoiler: I wasn't gonna do another one of these, but.... (click to see content)
I actually was gonna start off with this one, but I got caught up in the moment with the other two stages and couldn't help myself.
There's no deep lore to this. I was looking for things to try and make MAME cheats for, came across Arcade Quartermaster's site, checked it for interesting looking beat em ups, saw Pu-Li-Ru-La, and put a pin in it for stage making.
The back wall's interesting. I initially really didn't want to rip and code it (a wall of eyes with different animations for many of them), but my stage absolutely had to have it, so I sucked it up, X/Y position modded the BG and started to rip the 1st frame. The animations freeze on me and keep freezing. ...."Huh. Did I break something?" (because sometimes you accidentally make things write to 2, 4, or 8 bytes instead of 1 or 2). I go poking around some more, but I'm not able to find anything else that affects the animations, so I decide to look at the values of the addresses for the X and Y position of that layer. Turns out it's a large tiled image and all of the different eyes on the screen are animated through X/Y position shifting.
The darkness effect's a different story. There's probably some stage equivalent of remappal, but I ended up using a solid black image that'd jump to invisible and fade back in using AS128D___. In Pu-Li-Ru-La, it's because Jack O' Colson's fire attacks light up the stage, but I felt he'd have to be a stage hazard if I was going to have him do that, so no cameo from him. My choice of simply having the stage doing that with no explanation also didn't seem out of place, considering the other weirdness in the game.
As I was making the stage I saw that someone else had already made it, which bummed me out for a bit and then I felt silly about letting that bother me (especially because I remade one of my stages despite a million different better versions of it existing). It turns out we both had different ideas for our stages and took different paths to realize them.
tl;dr: My stage has 2 animations using single images (with one of them being pretty cool how it was done in the source game). Also, don't worry about making something that's already been made.