Shocking Discoveries

[Darkstride]

Start by equipping low-level gear, or switch to a different class.

Or just auto-attack as a mage class.

If nothing else works and you've levelled all your classes already, blue mage's power level is particularly tied to their equipment.

With Blue Mage you don't even need to deal any damage, you could just use Tail Screw to drop them to 1HP or spam Missile and keep halving their HP.

Aside from that, see if your Chocobo can smack them once without killing them. Or equip a very low iLevel weapon.

Lastly, try a Poison Potion and trap them once it eats away enough HP.