Fusion is the process of merging two separate beings into one, combining their attributes, from strength and speed to reflexes, intelligence and wisdom.In the anime,atleast five characters fused.
Goku+Vegeta=Gogeta
Goku+Vegeta=Vegito
Goten+Truns=Gotenks
Kibito+Supreme Kai=Kibito Kai
Piccolo+Kami+Neil=Kamicolo(Commanly called Piccolo)
Tell us which one is your favorite.