Pernico?

The young son of hades padded grumpily down the dark New York street. Of all the gods he had to get on Hecate's bad side. Grass sprouting between the path wilted as Nico cursed at the world. Walking past the hood cap of a car, Nico realised just how ridiculous and embarrassing his plan was. He stood and stared at his reflection. Stood before him was a cat. Yes, you read that right, Nico had been turned into a cat by an extremely miffed goddess. If he could of face-palmed he would of but alas he couldn't. The source of the magic was a neon green collar around his neck. It stood out brightly against his black and grey fur and was just so tight that it couldn't be removed but wasn't choking him. His only hope to getting of the blasted thing was the Hero of Olympus and his long time crush - Percy Jackson