In case you haven't realized yet, Altered Beast is difficult. It was released for arcades way back in 1988 and then ported to the Genesis the following year, so it contains that near impossible old school side-scroller difficulty. I don't care how good you claim to be, you're going to need all the help you can get.
Want to jump around the different levels at will? We can help you with that! At the main title screen, hold the B button and press Start. This will take you to a special options screen. Once there, choose the round that you wish to go to and hit Start to return to the title screen. At that screen, hold A and press Start.
When I was younger, I used to have a blast messing around with videogame sounds using the built in sound test in the options menu. Years later, it's still just as much fun. From the title screen, hold A, C, UP, and RIGHT and hit start to access the sound test.
There are four different creatures you can transform into in Altered Beast and they change with the levels. However, by holding down A, B, C, DOWN, and LEFT and hitting Start on the title screen, you're taken to a screen where you can choose which beast to turn into in each level.
These can't be classified as cheats because they're more of just general hints, but they should still help.
There are a few parts in the game where it seems like you should be able to jump higher. Guess what? You can! Simply hold UP as you hit the jump button and you'll see a noticeable difference in your height leap.
A lot of people don't seem to know that Altered Beast supports two players. Just hit Start on the second controller to have a buddy join in. It doesn't excatly make it a party game, but it can be a blast for couples.
This one doesn't actually halp, but it is a lot of fun. After you rescue Athene and complete the game, you can attack the credits and knock them away.