Well, do you have the Bone Village Commerce shop? If you do, get a punch materia ( magic punch, gioblin punch, iron punch, iron fist) and buy a Summon DMW materia from the BOne Village shop. Fuse them adnd you get costly punch, which does 99,999 damage every shot provided your HP isn't over the max.
Also, if fusing any 2 materia plus 99 phoenix downs = +999& health. Thats where Minerva becomes very useful =]