Slinky Pie is Pinkie Pie's little sister. Her name came from how thin she is. Alot of ponies think she is a boy, but if not, they call her ugly. She is a very good spy. She doesn't care about joining the Cutie Mark Crusaders, she says "I'm not joining that babyish club! I can earn my cutie mark BY MYSELF!".
Though over months, she has seemed to get alot more happy and cheery.