Sega Master System Cheats - Masters Of Combat

Extra difficulty and enemies have no life:

Enter KEY as initials at the high score screen. This unlocks the Extra difficulty setting and a level where enemies die after a single hit.

Extra difficulty level, faster on NTSC:

Successfully complete the game under the Normal or Hard difficulty setting to unlock the Extra difficulty setting, and a "No Wait For NTSC" option, which makes the game run faster on NTSC systems.