Yuu Yuu Hakusho 4 Cheat Codes for Gameboy

Fight as Lei Zhang:
Select "Vs. 2P" mode at the main menu. Highlight Enki, then hold Select + B and press Right at the character selection screen.

Fight as Raizen:
Select "Vs. Comp" mode at the main menu. Highlight Enki, then hold Select + B and press Right at the character selection screen.