Diablos
Non - Elemental
Diablos is one of the better GF's. He is made up of thousands of bats and collecting them together he hurls a powerful ball of Demi at your opponent. The percentage of the enemies energy he takes off depends on his level. Also His Mug ability can be very useful for collecting items for weapons.
Before leaving on the mission to Dollet talk to Headmaster Cid. He will give you a magic lamp. Save before you use this as it contains the GF Diablos. If you use it you are put into a fight with the GF. Diablos is very powerful no matter what your level as his attacks use Demi. To beat him stock Demi's from him and then using Double cast it back at him. When the Demi's stop taking off much energy revert to using GF's and hopefully you will survive