So this one is a little different.

Basically come up with your own skill or skill upgrade for any class. Even create or describe the skill icon if you want.

I personally suggest that all healers Apr attacks should apply a certain debuff. WHM gets stun after all

Gravity - draws in all nearby mobs and applies slow.slowing down their auto attacks and cast times. (Fits with the whole gravity thing)

While the Art of War could be something that drains a mobs stats.

Tomahawk could apply a small bleed effect

While shield lob could apply concussion.

Unmend applies weakness to magic for a short duration

While Gunbreakers Lightning Shot applies weakness to physical attacks for a short while.

Of course the effect gets weaker and shorter when applied to the same mob.

A cross skill for casters "singularity" a target placed Aoe which opens a black hole to drag away and hold mobs in place for about 13 secconds (basically for solo play)