If you want a slightly easier way to approach the battle, kit everyone out in Mirror Mail and move out of range of his physicals (set your healing Gambits to use X-Potions). He will still spam spells, which will naturally bounce to either damage him or to no net effect. If you can keep out of his way but have the group close enough together to get area effect spells, Self: Scathe or if you don't have that Self: Thundaga (Fafnir, being an ice monster, is thunder-weak) is a fairly effective way to do large damage quickly.

This was my "lazy man's way" of doing the battle.