The end draws near...
Forsaken is an enemy ability used by Kefka in the final battle in the original versions, and also by Omega Weapon in the Advance and iOS/Android/Steam versions. It is Kefka's most powerful attack, with a spell power of 220, and deals unblockable non-elemental magic damage to the entire party at the cost of 20 MP. When charging up the attack, Kefka will say, depending on the version, "The end comes... beyond chaos..." or "The end draws near...", followed by an image depicting his laughing head, and then the screen will quake.
Forsaken appears during the final phase in the battle against Kefka in Sigmascape V4.0. He is seen charging a red aura before unleashing the attack for massive damage, which transitions the fight to a temporary phase with a different background, where multiple complex mechanics must be executed correctly by the party. Eventually, the effects fade away via broken shards. When he first uses the attack, Nero tol Scaeva says "He's gone beyond chaos... the end approaches!", alluding to the SNES/PSX version of Kefka's statement before charging up Forsaken in Final Fantasy VI.
Kefka uses Forsaken as part of his EX Burst, which activates when the button sequence is inputted incorrectly. When using it, he'll ask what his opponent thinks of his attack, and upon using it, will yell "C'mon, c'mon, c'mon!" When about to use it, the camera will zoom up to his face, alluding to Final Fantasy VI, when Kefka's face was displayed when beginning to charge the attack. In addition, it will zoom back to show Kefka and the opponent in a pose mirroring the final battle from the same game.
Aside from this, he also uses a variant for his standard attack called Forsaken Null.
Forsaken is a moveset used by Kefka as a summon. It turns the background red and causes a purple explosion. As this is going on, Kefka is seen with a contorted face similar to that of his laughing head icon as he's charging up the attack from Final Fantasy VI.
Forsaken means to be "abandoned" or "deserted".
Goner is a slang term meaning someone is about to die (ie, "he's a goner").
The Japanese name, "Missing", alludes to something that is lost or unaccounted for.