Early game, possible rematches in the midgame(Plus the Dream Pixer tutorial boss!), but never in the lategame unless he can use his undead form then.
TUTORIAL BATTLE
Pixer would start by teaching Wymar the controls, using Pixel Dummies to teach before teaching Wymar about bosses! That'd be it.
NOT TUTORIAL BATTLE
Pixer would notice Wymar and ask if she'd like to fight. When told yes, he begins! When told no, he begs her to let him fight, since he's been dying to fight someone who won't just kill him in a few seconds.
He uses his Pixelite magic, blasting out fireballs, ice balls, and even lightning balls!
PHASE 2
When he reaches phase 2, he turns red-hot! He can now burn through Wymar and deal BIG damage! He also gets stronger attacks.