A young fairy girl of unknown origin, C-Mond serves as the housemaid of the Imitation family, and is in a relationship with the unnamed young man of the household. Little is known of the Imitation family, outside of their distaste for science.
C-Mond and Mr. Imitation are infatuated with each other, and C-Mond wishes only to live with him for the rest of their lives. In fact, her sole ambition is to find her lover, who is said to have gone out to find the twelve Secret Stones himself - what his personal ambition is is unclear. Mr. Imitation is constantly referred to as "husband" by C-Mond, though this is likely just wishful thinking.
Being a maid, C-Mond is humble, caring and hardworking, and is never one to raise her temper. Her life appears to revolve around the wellbeing of her master, and she dreads the thought of him ever running off with another woman. She has kept a diary since she was young, and uses it to record her continuing quest to locate her "husband".
She has issues with her small stature, and as such takes offense to a lot of remarks, size-related or otherwise, though she merely remarks that such comments are mean - she's not the kind of person who would insult people back for insulting her.
Keeping a diary
C-Mond is found by a port near Baguette Lighthouse, waiting for her husband to return. Curiously, this location is named after a foodstuff rather than a gemstone unlike most of the other character and location names in the game.
C-Mond speaks in third-person in the Japanese dialogue; this was apparently lost in translation for the European versions.
C-Mond's name is unique among the characters in that it isn't simply a gemstone's name or a piece of it, but instead a strange mangling of it. The GBC version translates her name as "Seamond", and anything that's still pronounced the same way phonetically is still correct; it just boils down to personal preference.
So what is her name actually meant to mean? My best guess is that it's just stepping back a letter in the alphabet, from "D-mond" to "C-mond." I... I don't know. I'm clueless! Ask Taito!
C-Mond shows you how to play the game.
C-Mond searches for her master.
C-Mond searches for her master. Again.
C-Mond teaches a panda croquet. Wait, no, she's searching for her master again.
C-Mond's attack pattern is to fill the five centre rows, and one on each side. Functionally similar to Garnet's, this is very efficient at filling the enemy's screen, a good defensive option. However, the two gaps present a nasty weakness for the enemy to exploit.
When facing C-Mond as an opponent, aiming the ball into the gap between rows will give you a perfect spot to bounce away at them, breaking through them easily.