Before taking on Death Gaze the party level should at least be in the mid-fifty range. Lower-level parties may want to equip Protect Rings and cast NulDeath to protect against Death Gaze's spells.
The party should cast Protera and Invisira to defend against Death Gaze's physical attack. Haste and multiple castings of Temper are necessary to deal decent damage due to its high Defense. After casting Haste and several castings of Temper for each physical attacker, the Black Wizard should attack with Firaga or Flare, preferably using the Judgment Staff for free castings. The White Wizard should attack with Diaja or Holy, or the Masamune if they have it equipped.