The description given of this ability is as follows:

Twofold melee attack.Combo: PGL WS 7, Bonus: Chance to render target unable to use weaponskills.
However, the skill's placement in the list (or, its indentation, rather) seems to indicate that it links from PGL WS 8. I think linking it from 7 would give us the only four-tier combo in the list, so I'm kinda leaning towards WS 8, myself.

Anyway, just trying to squeeze as much info out of this post as I can. Thanks for the help.