The Mors is an enemy in Final Fantasy IV: The After Years. It is weak but if attacked physically it will heal itself if the blow did not defeat it. If not killed fast enough it will retreat. Mors are highly valuable enemies as they provide a lot of EXP for relatively little danger, assuming the player can defeat them in one blow.
Mors is the Latin word for "death". The enemy's name is most likely a mistransliteration of 'Molds', as its name in the Eastype version of Final Fantasy IV (exclusive to Japan) was 'Floating Mold'.