Just a quick note if you are boosting online and going for the Mad Destroyer and Death on the Battlefield achievements.
-One person should be Yun-Seong
-The other can be whomever.
-Use his forward-Y-Y attack on the other person, who should be blocking the whole time, until a Soul Crush happens.
-Critical finish, repeat twice.
You can also take turns if you both are boosting to level 20. Just switch who is playing Yun-Seong every level. Me and my boosting partner both hit level 20 pretty damn quick.
Looking for boosting partners in the following games:
-Left 4 Dead
-Injustice: Gods Among Us