To me knowledge Metal Slug X came after Metal Slug 2 and was also released for the NeoGeo AES, not sure if there was a home version, be surprised if there wasn't. They are basicly the same game. The PS1 version of MSX is a port of the NeoGeo arcade version. Shame to hear the CD version has slow down as MS2 is my favourite MS of all.
1. This game seems *related* to "Ninja Combat". It's basically the same game, only Ninja Commando is overhead and Ninja Combat is side scrolling. It's made by the same company, and each game has a "Joe" character that *might* be the same character. There's also the useless backflipping button, and a million other little things that lead me conclude the two games are related/connected somehow.
2. The main villian in Ninja Commando looks just like the "Let's Dance" era David Bowie!. In fact, if you think/pretend the game's main villian IS 1980's David Bowie, the game takes on a whole new camp-humor and charm.
Ninja Commando is part 2 of Time Soldiers
allso metal slug x did come after metal slug 2 part x has all the slowdown part fixed from part 2
and yes metal slug 2 and x did come out on the neogeo home system (AES)