A combination of the words Revenge, and Vengeance.
Revenge means the desire to inflict retribution. Vengeance means the act of killing, injuring, or harming someone because they have harmed you.
Revengeance takes these two words and combines their definitions into one, the definition is the desire to kill, injure, or harm someone because they have harmed you to inflict retribution.
He had gotten harmed by a bully at school, and to get his retribution, he got back at him by injuring him more severely in his Revengeance.