Screwball

Screwball, also sometimes known as Topsy Turvy, is a curious anomaly of a pony. She is very closely associated with Discord, who was in some way or another directly responsible for her existence in The Return of Harmony Part 2. She later makes a cameo in the official My Little Pony: Friendship is Magic comic book series by IDW, where she scares some cats, showing that she remains a curious anomaly of a pony even after Discord's defeat.

In fan-fics, she has been portrayed as a devotee of the Draconequus and sometimes as his right-hand mare or harbinger. Alternatively, she has also been portrayed as an unfortunate victim, transformed into a being that is not wholly equine but not inherently bad enough for the Elements of Harmony to automatically fix.

Role in the Series
In the SAF Chronicles series, Screwball makes her first appearance in Project Nosferatu, where she is portrayed as Discord's subconscious dream friend who has been around since Discord was 3. She enjoys Discord's company so much that she gets extremely bored when he wakes up from unconsciousness, and leaves. Screwball is also capable of escaping Discord's subconscious in some instances where his chaos grows stronger, as seen in The Return of Harmony Part 2. Aside from that, she is a crazed pony who lives in Discord's mind all day, and therefore has little knowledge of what goes on in reality.