Here are my creations:
Name: Chibigotchi
Stage: Baby
Looks like: Smaller version of Marutchi but black with arms. Shirochibigotchi will be white with arms.
How to get: Get a baby. Simple!
Description: Cute loveable baby boy (for boy) and sweet little baby girl (for girl)
Name: Mamemitchi
Stage: Adult
Looks like: Mametchi with big ears and big feet.
How to get: Treat it really well, only let the happiness hearts drop down to 2 once and don't let the hungry hearts drop down more than once ever.
Description: A little genius with an IQ of 225 (halfway between Mimitchi's 200 and Mametchi's 250) and is very sincere and polite.
Name: Obake-Chi
Stage: Death
Looks like: Obake-Chi from Tamagotchi Angel (the spirit next to the grave).
How to get: Don't treat your Tamagotchi well at all, so badly it dies early.
Description: You didn't treat your Tamagotchi well did you? Well, you're rewarded with this spirit from its grave... treat your Tamagotchi better next time!