Giant Rat

Giant Rat is a boss in Final Fantasy III. It is found in the last room of the Nepto Temple, and has stolen a ruby Nepto Eye from the statue of the Nepto Dragon.

Strategy
Use level three spells, two of which should be enough to take out most of his health, then use two level one spells which should kill him. If Desch casts Thundara, you've won.

You're going to want to be about level 10+ ideally. You'll be in Mini form, so the only people that are going to be able to do major damage are your Mages. So, you'll want their magic to be as powerful as possible.