Mercedes

It's extremely strong and grants invincibility frames. It also doesn't push enemies.

It's the equivalent of unicorn spike except you move forward instead of staying in the same spot,

Well, Unicorn spike haves some debuff effect which Lighting edge doesn't and it's stationary so you can continue attacking right after using the skill instead of repositioning yourself in some cases. Personally, I'm about to put the skill on a solitary corner of my keyboard and probably only use it when dealing with boss like mobs (LHC if I ever manage to find a party) and that's if I even remember about the existence of the skill when the time comes.

Shame though, Lighting Edge animation looks badass.

Anyway. I need to know what skills replaces what! Seriously, my keyboard is cluttered. Does Ishtar's ring ever replace stunning strikes? Is high kick demolition obsolete after getting rolling moonsault (I hope not)? How useful is Spike Royale? etcetc.