Dark Sun Gwyndolin

Dark Sun Gwyndolin is the leader of the Blade of the Darkmoon and an optional boss. He is voiced by Harry Lister Smith, who also voiced Prince Lothric in Dark Souls III.

Location
Dark Sun Gwyndolin guards the honorary tomb of Lord Gwyn in Anor Londo. The tomb can be found by using the spiraling staircase on the rotating bridge (while the bridge is in its lowest position) and descending to the second accessible bonfire. If the player wears the Darkmoon Seance Ring in this location, Gwyn's statue will vanish and Gwyndolin's fog door will be revealed. The player can then either pledge allegiance to him and his Blade of the Darkmoon or dare to trespass the fog door behind of which he dwells in, thus commencing the boss battle.

If the player doesn't yet have the Darkmoon Seance Ring, they can kill Gwynevere instead, which at that moment will be revealed to be just an illusion set up by Gwyndolin himself. The entrance to Gwyndolin's boss room will be accessible at the same aforementioned location.

Plot
Gwyndolin initiates players into the Blade of the Darkmoon Covenant. He accepts Souvenirs of Reprisal in exchange for increasing the player's rank in the covenant.

Lore
Gwyndolin was the last born son of Gwyn and the only true remaining deity to guard Anor Londo. He was raised as a daughter due to his strong affiliation with the moon's power. He uses the illusion of the princess, Gwynevere, to help hide his repulsive appearance.

In Dark Souls III, Pontiff Sulyvahn and Aldrich, Devourer of Gods travel to Anor Londo and capture Gwyndolin. Gwyndolin sacrifices his own life and allows himself to be devoured by Aldrich to protect Company Captain Yorshka. Aldrich then took on an appearance of Gwyndolin's upper body, having absorbed his powers and abilities as well. Aldrich also aquired Gwyndolin's last thoughts, a "dream" of Crossbreed Priscilla (or Yorshka) ("...[Aldrich] perceived the form of a young, pale girl in hiding.")

Strategies
The fight against Gwyndolin takes part in a seemingly never-ending corridor.

He's not a very difficult boss if the player has decent dodging skills. Of his three attacks, two can be avoided by hiding behind a pillar, while the last is strong and fast moving (he will tend to use the Sphere Shot after Orb Spread if you are hiding behind pillars). The main issue in the fight is really catching him, as he teleports away when the player approaches (equipping the Ring of Fog may increase the time available to hit before the teleporting animation), thus the best time to run up to him is when he's just finishing off his Arrow Spread, as he takes a few moments to recover. Gwyndolin can still be damaged during teleport and for a split second after actually moving, so it is possible to do considerable damage while the boss is still moving.

Both the Orb and Arrow Spread attacks are avoidable by hiding behind one of the pillars on either side of the corridor. The Sphere Shot, on the other hand, will go through walls, inflicting full damage if not blocked or avoided. The Orb Spread and Sphere Shot are magic-based, though, so a shield that can block 100% physical damage and has good magic resistance, like the Crest Shield, is recommended for this fight.

While devastating, both the Sphere Shot and Arrow Spread attacks have no tracking whatsoever and are easily avoided simply by running diagonally. If a player doesn't want to risk it too much, a good strategy to catch up to him is by moving from pillar to pillar, until they are about two pillars away from him, and then wait until he shoots his Arrow Spread. This attack can consist of two-to-four arrow barrages. Wait until he finishes the second one and go for him, if he shoots any subsequent arrows, dodge them by running diagonally.

Upon entering the tomb, Gwyndolin will teleport away. It is possible to move closer to him to a point just outside his aggro range. Then by equipping the Hawk Ring and using the Dragonslayer Greatbow, you can easily defeat him from range without him retaliating.

Arrow Spread
Gwyndolin will slightly raise up and shoot multiple arrows at the Player. Blockable as they do not use much stamina. Alternatively, the Player can stand behind the pillars so that the arrows hit the pillar instead. From New Game+++, if all the arrows hit a non-blocking player, death is certain.

Orb Spread
Gwyndolin will charge up his catalyst and shoot a cluster of homing blue orbs at the Player. Deals heavy damage if they connect. Recommended action is to hide behind the pillars as the orbs cannot go through them, or roll under it.

Sphere Shot
Gwyndolin will charge up his catalyst and shoot out a huge magic sphere which travels at great speed. Possible to dodge by rolling to the sides or directly under it or blocking with a good magic shield. The sphere can pass through the pillars, so hiding behind them is not recommended.

Trivia

 * Dark Sun Gwyndolin's boss fight has the same soundtrack as the Moonlight Butterfly.
 * Visible on his cloak and underneath it, Gwyndolin does have breasts despite identifying as male.
 * If Gwyndolin is fought before defeating Ornstein and Smough, Knight Solaire can be summoned from his usual spot. While he will not enter the arena to aid the player in the battle, a Sunlight Medal can be acquired at the end of the fight.
 * If the player uses the Darkmoon Seance Ring to enter Gwyndolin's chamber and kill him without destroying the illusion of Gwynevere, both Gwynevere and the illusion of sunlight in Anor Londo will persist after his death.
 * Should the player have a white phantom summoned, there is a bonus cutscene when they walk through the fog.