I never played Altered Beast beyond the demo that they had at the store, but it looks like there wasn’t that much more to it than what you saw there. It only has five levels, and that’s at the maximum; some ports included only four. Originally an arcade game, it was ported to many systems, but it was probably best known for being the game originally packaged with the Sega Genesis. You play a centurion who’s ordered by Zeus to rise from his grave to rescue his daughter Athena.
Along the way, you fight various enemies, and collect Spirit Balls that make you more muscular. After collecting enough Spirit Balls, you turn into an animal.
The main boss is a demon named Neff, who makes his home in the city of Dis, and takes different forms in order to fight the protagonist. Why “Neff,” I couldn’t say; I don’t know of any tradition of a demon by this name. Of course, the designers are free to invent their own characters, but I just find it a little strange that they’d use classic mythical figures like Zeus and Athena while making the enemy someone new.
The plot of the game also raises other questions:
1. Why does Zeus need to bring this guy back to life to save his daughter? Weren’t there any living heroes he could call on?
2. Why does Zeus sound like Elmer Fudd? Yeah, I know voice synthesizing was rather primitive back then, but it’s just funny that the Lord of Olympus seems to have a speech impediment.
3. Athena needs to be rescued? She’s, like, the most bad-ass deity in the Greek pantheon. Sure, everyone makes mistakes, but couldn’t they have picked a damsel in distress who couldn’t have easily kicked Neff’s ass without the help of some undead he-man. Or a young angel with a bow and arrow, for that matter.
4. I’ve read that the protagonist is supposed to be a Roman centurion, so wouldn’t he know the two deities as Jupiter and Minerva?