There's a TV show that I watched when I was a kid about a guy having a pet green monster that had two horns and was named Brock. (It's not Pokémon) The monster originally belonged to his grandfather. Later something happened to the monster and he got wings.
I also remember the main character having brown hair and there where two other people with him. There was one time where they went to the Ocean and they took out the monster and the people knew it was the grandfather's and thought he stole it.