Location: Hogwarts
Harry is walking in the hall when a portal appears out of nowhere.
Star Butterfly exits the portal and puts her Dimensional Scissors away, she then pulls out her wand, Harry does the same.
Harry: Avada Kedavra!
A green energy blast comes out of Harry's wand, but Star quickly dodges.
Star: Bacon Kitty Hawaiian Nightmare!
Star's wand shoots a blast of three-eyed kittens, bacon, and pineapples, which hits Harry
Harry is pushed away and starts casting several non-verbal spells.
Star dodges the spells
Star: Narwhal Blast!
Star's wand shoots multiple narwhals.
Harry counter attacks with other non-verbal spells, he then disappears
Star wonders where Harry hand gone, Harry then reappears and strikes Star with a spell.
Star: Glitter Whale Battering Ram!
A whale comes out of Star's wand, huge and bulking.
Harry: Confringo!
The whale explodes and Harry puts on the Invisibility Cloak
Harry: Stupefy!
Star dodges
Harry: Levicorpus!
Star dodges again and hits Harry with a Narwhal Blast. Star plans to keep the routine up, but Harry's not an idiot.
Star: Glittery Heart Slap Blast!
Harry is blasted against a wall by heart shaped energy that takes him back.
Star casts another Glittery Heart Slap Blast.
Harry: Reducto!
The heart gets disintegrated mid-blast.
Star: Laser Beam Blast!
Star's wand shoots a white laser that pierces through the air.
Harry: Protego!
The lasers are deviated. Star shouts out her next spell in quick succession.
Star: Rainbow Fist Punch
A rainbow punch hits Harry in the face and Harry tumbles back.
Star: Rainbow Blast!
Star's wand shoots a rainbow with hearts and winged bunnies and it spirals toward Harry.
Harry dodges and attempts to shout another spell.
"Avada Kedarva!"
Harry Stares in awe as Star forms a powerful airy shield around her, and the spell bounces around, fizzling out.
Star shouts the time freezing spell, and everything around her instantly stops moving, every little thing.
She smirks and shouts Dagger Crystal Heart Attack spell, ending Harry's breathing and the battle.
Honestly, this fight could go two ways, but Star could easily take the upper-hand as easily as Harry could.