I couldn't miss the chance to practice my drawing!
The Sylph glitch is a glitch found in the SNES and Easy Type versions of Final Fantasy IV. To activate this glitch, the player must simply rearrange Rydia's spells so that the Sylph summon is in the upper right-hand corner; whenever the spell is cast henceforth, it will cost 0 MP.
Also, a similar glitch is present in the Wii version: If the player places Rydia in the very bottom position of the party, the Sylph summon will cost 0 MP.
In both cases, the player must still have enough MP to cast it, even if no MP is expended, or the spell will be grayed out in the spell list.