Honestly I once got to the point of making your own custom heroes and I don't even remember how I did it, it was an accident.
My favorite is experimenting, I must confess. Throw various characters in there, see what they do, give them various tasks, objects, personalities, or foes and see the outcome. Also, I learned that you can overfeed them.
I had a Larfleeze going around and trying to take all he could, including food - And before I knew it I had a "chubby" Larfleeze. Man that gave me a good laugh.