One move that I found making the towers and pits a LOT easier when playing alone is the super punch. I didn't even know how to do it until I accidently pulled it off.
What you do is move slightly backwards with LS, then hold in LT. Your character will charge up a punch, at which point you can move in whatever direction you want. If it hits it sends almost every mob (except big brutes and Mother+Father) flying, knocking down anyone in the way. Works very well in crowded areas, or in the pits to send someone flying down floors.
I recommend mastering that move, as it helped me a lot with the challenges.