I usually roll Magus/Lucca/Robo for the final battle. Omega Flare can kill second form Lavos in five to six casts; With a Gold Stud to soften the blow of the 20 MP requirement of Flare as a variable, you're looking at very minimal MP recovery overall. Final form, focus down the left bit with physical attacks from all three characters. Defence drops, Magus uses DarkMatter and Robo/Lucca for Double Bomb which hits like a truck. You'll only have to muscle through three casts of Active Life at the most.