Vile in the first Project X Zone game can switch to his turn in a counterattack including a surprise special move after destroying his ride armor. In Project X Zone 2 he has higher attack power as Vile Mark 2 his map attack the most devastating combo chain up to 50 to 60 hit multipliers of damage. Sigma has greater stats with his higher defense and xp scratch ability his worse arsenal. The only reason it didn't get any harder is that the developers forget to give Project X Zone 2's final boss to revive respawning the villains, and never even before after it awakened.
Like that is objectively correct however in my experience Vile & Sigma in Project X Zone 2 were nothing more than a speed bump that barely effected me because I'm convinced this series was designed by people that wanted to appeal to people that hated SRPGs & why there was no challenge, it was just a mindless slog that wasted my time but I'm engaged because it weaponizes the IPs I hold dear to me so it's why I can't simply ignore it & regarding the final boss, Byaku Shin, it has one gimmick that is the perfect representation of this series (deagatory) which is the lower it health is, the less damage it takes & that increases my frustration but at least I managed to exploit one equipment that counter attacks an enemy ignored the garbage defense mechanic leaving it at one HP like this series is advanced bad to me for good reason, heck I got so much I can go over but I'll save it for another time