Vendetta brought the fiend to show and tell. She had it in a box. She released it after Charlotte's presentation of Buttons, her hamster. The fiend took Charlotte in its tentacles and went out to the schoolyard. Charlotte thought it looked like a monkey. Just when the fiend was about to eat her, the Giant Kitty scared it away.
Background information
In web episode 2, which is the episode "Charlotte's First Day" is partly based on, Vendetta brought a red monkey for show and tell.
In the end credits, the fiend was called "fiend from box".