Altered Beast is originally an arcade game. In each level, the player must collect 3 powerups in order to transform into a powerful beast and fight the boss of that level. This game was one of the first games of the Sega Genesis system, and was first bundled with it.
This might look like it's an auto-scrolling game, but in fact the scroll speed depends on the number of enemies on screen. The player tries to kill all enemies as soon as possible to increase the scroll speed, using 2 characters to maximize this process. Almost 30 seconds were saved compared to the previous version.