You know the Mantledrake in that video is level 65+ right?
To unlock that fire column spell it has to be level 35. But even then, based on my experience using level 29 mages with much better magic stats than Mantledrake (albiet using different spells), I doubt he could one shot most enemies in Metal Zone 2 at level 35. Not to mention the base activation of that skill is 30%, so you need a ton of skill ups to get it to go off consistently.
I mean it looks really useful, but it seems like it would take an insane amount of grinding to get to a point where it could actually work, and doesn't seem in the realm of possibility for the average player. For most people, getting someone who can inflict sleep or paralysis is a much more realistic possibility (albeit, less effective).
Edit: Didn't see the end of the video where it shows both Grace and Mantledrake are level 70.