First I will have to say that I have a lot of content to go through in the game, and am not aware if it already exists as a mob ability, but I remember in previous FF games, this spell was a great ally, and an even more powerful foe.
For those unaware, the spell typically rendered the target as "Stopped in time" meaning not only can they not act, with the ATB system of old, it would no longer fill until the spell wore off. In this game, this would translate to if you are inflicted with Stop, all of your gcds stop right in their tracks along with your inability to perform actions and move.
It differed from petrification in those games by still being able to take damage. In some previous FF games, if you petrified, you no longer take damage, but some bosses were nasty, and could crumble you causing KO (a mechanic I would like to see). Another difference between Stop and Petrification was if the last remaining player is stopped, the fight is over.
As an ability, I remember how much I loved using it on those regular mobs with ridiculous amounts of HP. It made the grinds just a little bit easier to deal with. I think implemented somehow in this game can follow the same suit. What do you think?