Several people stared at the trio as they walked down the street, comenting on their incredible costumes. Kat looked at a couple and thought about changing them, but they really didn't spark any ideas. Then she saw the horse. It was two kids in a goofy-looking two-man horse costume, looking even sillier because it was too big for them. The two boys inside were arguing with each other, stumbling because they wouldn't work together. They sounded pretty young, maybe 11 or 12.
Kat walked over to them, her freinds following curiously. "Neat costume, guys. Wanna make it look really wicked? I can fix things so you are a Nightmare, a black demon horse that will spread terror as it breathes fire and sucks humanity from souls."
The boy in back snorted. "Bullshit! You can't do nuthin' to this stupid costume to make it less stupid."
Kat grinned and came up with a more elaborate spell, which she cast with a flick of a wrist and some mumbled words. "No, not bullshit. Horse shit." She reached out and patted the horse's 'rump' and giggled as the tail lifted on it's own and a very real-looking anus pushed out very real-looking manure.
The boy in back gasped. "What happened!?" The middle of the costume parted and he stuck his head out of the side, still holding onto his brother's waist.
"You get to be the other head." Kat squatted down and rubbed his face with both hands. Before the boy could pull away, his skull seemed to deflate and his head elongated. At the same time, the costume's fake fur changed into glossy black hide that swept from the rump forward. Kat let go and stepped back, letting what was now a thick black horse cock fall and then draw into a large sheath between fully animal hind legs.
The boy in front tried to yank free, but he was already part of the new equine body. His scream turned into a blood-curdling whinney as what had been two boys in a costume was now a very real Nightmare. The huge horse-like demon's eyes glowed red and it snorted a short burst of fire from its nostrils.
Kat pointed down the street. "Lots of kids down that way - sweet souls waiting for the humantiy to be sucked out of them. Donlt make them all horses - I like a little variety."
The massive black stallion trotted in the direction indicated, tail lashing. Kat grinned. "Wonder how many kiddies will want to ride the pretty horsie?"