All you do for this is combine aspects of other genres and make a new, totally cool genre of music. Don't forget to give it an awesome name too.
You can make as many music genres as you want, but make sure the genre doesn't already exist!
My genre would take many aspects of Grindcore, heavily distorted, down-tuned guitars, extreme tempos, etc., and have nursery rhymish lyrics.
I would call this genre ToddlerGrind.