Gex

Gex Codes from Little "D"
Final Battle Code-CZYDRHYP
Stage Skip-At any map screen press start and then hold R shift button and press start right right down right up L shift button A left left!

While in any stage press start and enter any of these codes-

99 lives-Hold R press up up down right A down
Invincibility-Hold R press B A down A down down down up down right
Fire Shots-Hold R press C up right right Y B up right up
Ice Shots-Hold R right Y right down right right B left up right
Electric Shots-Hold R press down up start right right Z A start start
right right High Jump-Hold R press down up start right right down L right start
Super Speed-Hold R press right X L right A down start right right down

Level Codes from BoZo
TXZFKHGP - Cemetery, Stage 4, "Disco Inferno"
CYRFYHGP - New Toonland, Stage 1, "Twin Towers"
BYTCYHGP - New Toonland, Stages 2 and 3, "Pow!" and "Rock It!"
CXGCSHKP - New Toonland, Stage 5, "The Flatulator" (The boss)
DXHCSHKP - Jungle Isle, Stage 1, "Feeding Frenzy"
TXKLPHKP - Jungle Isle, Stage 2, "Congo Chaos"
DXBLPHKP - Kung Fuville, Stage 1, "Sumo City"
HZVYRHKP - Rezopolis, Stage 1, "Rez Knight Fever"
CZYDRHYP - Rezopolis, Stage 3, "Rez' Lair" (The final boss)