I couldn't finish 'em. Looks like this's gonna get complicated.
The Wave Cannon is a boss exclusive to Final Fantasy V Advance. It is fought in the same battle as with Guardian. During the battle, it will spend several turns charging up, and then use Wave Cannon twice. As Wave Cannon deals half each character's maximum HP in damage and inflicts Sap, this will wipe out the party, and so it should be taken out quickly. One or two castings of Bahamut is more than enough to dispatch it.