E.V.O.: Search for Eden Cheats
SNES Cheats
Human body
After becoming a mammal, evolve the cat jaws and rabbit body. Then, select the Ramopithecus body. It will become human after two more evolutions.
Mermaid body
Accumulate 10,000 evolution points by the final ocean stage of Chapter 5. Select "Hand and Feet" when evolving your character, then select the "Try To Evolve option". Continue to evolve three times to become a Mermaid.