So i just go drill cannons, from the description, it says you can get more dmg if target is petrified. is level 5 petrify required for this?

on level 5 petrify description it says : Petrifies all enemies in a cone before you. Chance of successful attack is low. Enemy level must be a multiple of 5. Has no effect on enemies whose level is higher than your own.

so this not sound very reliable, any thoughts from more experienced blue mages on this? i still didn't get the spell yet, i tried to solo the dungeon and failed so far. will try when i get more levels.