When your low on MP and have the HP<--->mp materia equip it and you MP can sky rocket up to 9999mp (max) then heal your HP (which will be at low since you didn't have mp when you equip it) with cure. When your hp (999hp max) is full take off the HP<--->mp materia and you should have full mp and you can cure your HP back to good status. I just was thinking of this while re-reading this thread its pretty handy and I'll probally use the materia myself just for this purpose. goodbye ethers.