Never fear, for Dark Arts is here (again) to fill up the mp dump gap that edge/flood left. Dark Arts was a case of a fantastic concept that was implemented poorly, and deemed bad design when it was actually quite genius. This time around, a couple measures will be taken to ensure that the new version of Dark Arts doesn't go out of control like it did in 4.x. The first is to simply reduce DRK's mp generation overall. Previously, DRK's mp restoring effects restored mp in increments of 1/2 or 1/5 the mp needed for one Dark Arts. Perhaps you can see the problem that those amounts don't line up nicely, which caused your mp to not quite line up with your mp costs nicely. To fix this issue while also tuning down the mp generation, all mp restoring effects will now generate 1/3 or 1/6 of the mp needed for one Dark Arts, which is now 1000 and 500. The second measure is to remove Dark Arts effects from all abilities not on the GCD. This should be self-explanatory. This resulted in forced double weaving too often with Dark Arts and Carve and Spit, and also breaks the second rule of "no buttons should make you press other buttons to get their effect" with the one exception being Dark Arts affecting abilities on the GCD.

Spinning Slash and Power Slash are back, more on those later

Mechanical Changes
Darkside now increases damage dealt by 10% and reduces spell/weaponskill recast times and auto attack delay by 10%
Blood Guage now fills up to a maximum of 120

Action Changes

Syphon Strike now has a potency of 280 and restores 1000 mp on hit

Soul Eater now has a potency of 380 and generates 10 blood on hit. Dark Arts potency: 500, Dark Arts effect: restores hp equal to damage dealt (cure potency 500 might be effectively the same?)

Unleash Identical except it now costs 1000 mp