Coco Bandicoot is Crash's sister. She is a mutated animal created by Neo Cortex. In Twinsanity, she gets put to sleep by Cortex, who then disguises as her to lure Crash into a trap.
Later on, she sneaks into the Psychetron as Crash and Cortex return from N.Gin's battleship and attacks Cortex, ruining their efforts to use the machine, aswell as freezing her once more for the rest of the game's events.
Gone a Bit Coco
Alternatively, the machine's malfunction would've opened a portal into her brainovial hyperbarium, which Cortex describes as "The well where her personality springs like sugar water."
Cortex would've then entered the portal out of sheer curiosity, but the events inside are unknown.
The level "Gone a Bit Coco" would've taken place there, but the level was scrapped due to technical reasons.
Coco's voice actor is Debi Derryberry.
"Ha ha, I'm gonna get ya, hihi. Come here!" - First FMV, Coco tries to catch a butterfly
"You monster! Let my brother go!" - When Crash and Cortex return to the Psychetron for the first time