Altered Beast

Altered Beast is Sega's Greek-mythology brawler: Zeus raises a dead warrior from the grave and sends him through five levels of underworld to rescue Athena, punching through waves of undead on the way. It was the pack-in game that launched the Mega Drive outside Japan, which is why almost everyone of a certain age knows 'Wise fwom your gwave' by heart.

The hook is the transformation system. Each stage hides white spirit balls dropped by two-headed wolves; collect enough and your warrior powers up through bigger muscles, and at a full set he transforms into a beast - werewolf, dragon, bear, tiger or the golden werewolf - each with its own screen-clearing attack. The arcade original runs on System 16 with sprites the Mega Drive version could only approximate, and it is short: five stages, maybe twenty minutes, tuned more as a spectacle than a challenge. The two-player mode lets a second undead warrior fight alongside you, and the bosses - from Neff's rotating-head forms to the multi-headed dragon - are the reason people still boot it up.

• ▸Five beast transformations, each with a signature full-screen attack
• ▸The spirit-ball power-up chain from wolf drop to full transformation
• ▸Simultaneous two-player brawling on System 16 hardware
• ▸Bosses built around the transformation gimmick, not just health bars