Altered Best (known as Juuouki (獣王記, Beast King's Chronicles) in Japan) is a beat'Em up developed and published by Sega. It was also released for Mega Drive/Genesis, Master System, NES, C64, Amstrad CPC, Atari ST, ZX Spectrum, Amiga, 3DS, Android, macOS, Switch, PS3, TurboGrafx CD/PC-Engine CD, Turbografx-16/PC-Engine, Wii, Xbox 360, PC, PS2 and PSP (the latter two as part of a compilation).

You are a hero raised from the dead by the god Zeus. You need to rescue Zeus' daughter Athena who has been kidnapped by the god Neff.

The game has auto-scrolling from left to right. You can jump, perform a high jump, punch and kick. You go through the level and need to power up yourself by killing a certain enemy, a flashing two-headed beast. Killing the beast will release an orb. If you collect it, your muscles become larger and your kicks and punches do more damage. Upon collecting the third orb, you transform into a beast with special attacks. In each level, you will transform into a different beast. When you reach the end of the level, Neff will await you. If you have transformed into a beast, he will transform into a monster and fight you. If you haven't transformed yet, he will leave and the level will loop. This continues until to you reach Neff in beast form.

The game can be played in two-player co-op.