Monster Party is one of those odd cases where a game saw a release in the US but not in Japan. It's hard to say just how the Japanese release would have been different from the US version, as I haven't found any screenshots beyond the halfway point of the first stage, but from what little I have seen, it looks like we got stuck with a dumbed-down version of the designer's original concept. Take a look at the title screens:
The most obvious difference is, of course, that the Japanese release has blood on the title screen where the US release gets green slime. It looks like something's up with that spider too, but the scan's not good enough for me to say for sure. Still, I imagine that a lot of the bosses were altered in some way or another. Take a look at the first boss, the man-eating plant:
The Japanese version gains what looks to be a karaoke machine (perhaps taking a cue from Little Shop of Horrors?) and a slightly different "face" to go with it. This explains the invisible platform to the right of the plant in the US release. The graphics were simply blacked out to blend in with the background, it would actually be a very simple matter to hack both the mike and speaker back into the game. Intreguing stuff.
Tinkering with the rom also shows that the third boss, the pumpkin ghost, had something removed from it's room too. A portion of the backdrop was dedicated to a large image that, like in the plant's room, was blacked out. A quick scan didn't turn up anything else, but that's not saying that the original Japanese designs weren't altered when the game was brought to the US, like with the man-eating plant.
Anyways, I'm really hoping a FC prototype of this game will turn up eventually. It's kinda ironic I've developed such a fascination with this game; back when I was a kid, I couldn't get past the first stage because it simply creeped me out too much.
Here's the US rom.
