Convert

Convert allows the user to switch their current HP and MP totals.

Final Fantasy XI
Convert is a job ability exclusive to Red Mages when they reach level 40.

In battle, this ability does create a moderate amount of enmity, so a Red Mage could gain unwanted attention with little to no HP to survive a hit with, but more commonly they are killed by an area of effect attack that hits the whole party.

Final Fantasy XIV
Convert is available to Black Mages.