Undyne

Undyne in Undertale (Or IS it..?) is one of the monsters affected by Sans's "accident".

Armoured
With her armour, Undyne looks the least glitched. If you look closely, you'll notice her legs's positions have swapped, her spear is glitched, and other changes.

Armourless
Possibly the second most glitched character in the AU, her armourless form is too hard to describe.

Papyrus
Undyne used to train Papyrus, until Sans's accident made Papyrus lose memory of who Undyne was.

The Human
Undyne tries to kill the human at first, but realises that they are trying to undo Sans's accident.

Trivia

 * Undyne without her armour is the second least glitched character (least glitch being Frisk)
 * Undyne's spear is the only notably difference in her with her armour without looking closely.