when your doing a team battle, you put goku and vegeta, or goten and kid trunks on your team, and when you get to five blast stocks you push the analog stick in a direction its different for every fusion and then press R3
All the classic characters such as Goku, Vegeta, Gohan and the rest, along with Freza, Nappa, Brolly, Cell, Buu, and just about every Dragonball Z character you can imagine