MP bug

The MP Bug is a bug in Final Fantasy VI that involves MP usage.

Control and MP Bug
The Control battle menu responds poorly to MP change. This bug deals with the fact that Control takes a turn or two at most. To notice a change in a monster's MP. Once the player has controlled a monster, wait for the controller's gauge to fill up, then try something like deplete the monster's MP. Looking at the menu, the player will see that all MP dependent abilities are still available. Not only that, you can still use them for one turn since they're attacks initiated from the Control menu which ignores MP cost in practice. This also works in reverse; for example, Control a Sprinter after having depleted its MP. Use its Special Attack Osmose Beak to replenish over 20 MP. On the controller's next turn, Cyclonic, the only MP costing attack in Sprinter's Control menu, will still not be available even though it gained sufficient MP from the previous turn.

Runic Absorption Bug
If a character uses a spell while equipped with the Gold Hairpin (halves the MP cost) or Celestriad (All MP cost is one) and Runic absorbs it, it will not affect the amount of MP that Runic absorbs. For example, a character equipped with the Celestriad cast Ultima will take 1 MP to cast, but Runic will still absorb 80 MP from the spell cast by a party member.