The Deathgaze is the mutated, winged form of the Yuke Veriaulde, who was subject to horrible experiments under his master Larkeicus. While Veriaulde was given eternal life due to this experimentation, this boon had one unfortunate side effect; Veriaulde would transform into the Deathgaze whenever he was exposed to a fragment, no matter how many, of the Crystal Core.
When the Hero and companions descend into the deepest room of the Ruins via levitating platform, they meet Veriaulde, who had been hiding away for centuries in order to prevent anyone from tempting the Deathgaze within him. He starts off a surprised and pleasant conversation with the heroes until the protagonist pulls out the Crystal Core piece. Veriaulde backs away in terror, but cannot stop Larkeicus' curse within him. In an insane fit, the Yuke morphs into the Deathgaze, which the party must fight.
The Deathgaze is a levitating creature, and only a character with Double Jump can reach it. It attacks with Lightning beams, which inflict the Paralysis status, and a wing attack. If a character jumps on top of it, the Deathgaze will cover itself in purple light, which does heavy damage. Casting Gravity at the beginning of the battle will drop its HP considerably, as well as pinning it to the ground. Breaking the casing around the diamonds on its wings will allow the player to damage its weak spot, and if one attacks the diamonds sufficiently, it will have a Gravity effect upon it.
The Deathgaze is also capable of casting spells such as Gravity and Thundara, so players must watch for its Target Ring to avoid being inflicted with Paralysis and Gravity. Gravity is especially dangerous, as players affected will not be able to reach the Deathgaze without the aid of Gravity itself.