Deathgaze is a boss from Final Fantasy IV: The After Years. Unlike the other bosses found in the Depths of the True Moon, it is a random encounter, as it was originally in Final Fantasy VI. After defeating it, the Dualcast ability can be extracted from the Dark Crystal. Only Palom, Porom, or Leonora can use it.
Oddly, it is not possible to lose this battle. If Deathgaze defeats the entire party, the player will be returned to the Depths, though with all five characters dead. If Phoenix Downs are not used immediately thereafter, the next battle will result in a Game Over.
Deathgaze will start off by casting Death on the entire party. He can then attack with a physical attack, Blizzaga, Thundaga, and Death on a single target. He will eventually run away, but his HP will remain the same unless the player leaves the floor.
Deathgaze is weak to Throw, so spears, boomerangs and the Jump will all deal extra damage to him. Deathgaze's attacks can hit fairly hard, but as he can run away, it is possible to flee from the battle if things go badly.
Black Mages should attack with Flare, or a level 3 elemental spell if it is not available. White Mages can use Holy to deal extra damage, or heal when necessary. It is good to exploit Deathgaze's weakness to throw skills.