My only advice is on his/her 3rd form, please, oh please be prepared to mostly cast spells on him/her. and have a good/powerful long ranged weapon. Falz is in invincibility mode 95% of the time. and only magic can pierce the shell. and when Falz escapes invincibility mode, he/she is usually across the stage and no where near you to slash with a striking weapon. that's when you should pull out your guns. if you're a Cast and without a gun, be prepared to be sitting there for at least a good hour. If you're a Force, its in a matter of minutes. seriously, it's that one-sided of a battle.
I swear this battle on ultimate is what my friend said: "98% luck, and 2% skill." you just got to get lucky hitting him/her with an actual attack. the stage is poorly built on purpose to make the battle difficult. curse that giant ring! D:<