I made this guide hope it helps everyone out.
For a text guide, you need the Pull ability I had it equipped to my
. To do this you need to lock on to a hostile then use pull by holding down the button you have it mapped to to then hold down
to stab them with the omni blade.
Update: As posted by Erwo the Elder in the comments, he was using a Kett Sword and the achievement did not track, however once he switched back to the Omni-Blade it started tracking again. Unsure if other melee weapons will void the tracking as well but better safe than sorry.