Seath the Scaleless is a blind albino dragon and late-game boss of Dark Souls, encountered first in the Duke's Archives, and later in Crystal Cave. Seath betrayed his own kind, the Everlasting Dragons, due to his lack of stone scales which granted the other Dragons their immortality. He aided Gwyn and the other recipients of the Lord Souls in their eradication of the immortal Dragons, ushering in the Age of Fire. For his service, Lord Gwyn granted Seath the title of Duke and his own special duchy within Anor Londo, as well as the resources needed to research sorcery-based immortality in the form of the Duke's Archives. During his research, Seath kidnapped many maidens across Lordran to be used as test subjects in his crystal sorcery experiments. When Gwyn left Anor Londo for his ill-fated mission to rekindle the First Flame, he entrusted a fragment of his Lord Soul to Seath, granting him additional power.
Seath's obsession with crystals and immortality eventually drove him mad, but not before achieving his goal of eternal life via the Primordial Crystal. The sorcerer Big Hat Logan expresses a unique admiration for Seath and expends great effort to reach the Duke's Archives for his own magical studies.
The first battle with Seath is unwinnable; it is suggested to either spend one's Souls beforehand, or equip a Ring of Sacrifice prior to death. Seath's first encounter in the Archives is also the only boss arena in the game that can be exited by the player through the fog door without killing the boss.
The second encounter with Seath is at the deepest point of Crystal Cave, where the player locates the Primordial Crystal. Seath begins the battle with invincibility; the player must break the Crystal in order to do any damage to Seath. Once he is vulnerable, simply attack the left or right tail of Seath and follow it as he attempts to recenter himself. Cutting off Seath's middle tail grants the player the Moonlight Greatsword, a rare weapon that deals damage based on the player's Intelligence.
Seath has a number of attacks, most of which cause Curse damage:
- Far Curse Beam - Seath will fire a beam in an arc around him, driving crystal spikes up from the ground which cause Curse damage.
- Straight Curse Beam - Seath will fire a beam straight ahead of him, driving crystal spikes up from the ground which cause Curse damage.
- Close Curse Beam - Seath will fire a beam directly in the ground in front of him, driving crystal spikes up from the ground which cause Curse damage.
- Crystal Curse Explosion - A very dangerous attack, Seath will spawn crystal spikes in a large radius around himself which cause Curse damage.
- Tail Thrash - When the player stays behind Seath for too long, he will spin around, slamming his three tails into the ground repeatedly. This attack is unblockable and makes cutting off Seath's tail very difficult while fighting him solo.
- Punch - Seath will punch and claw at the ground in front of him; this is easily dodged.