Dark Sun Gwyndolin is an optional boss you can fight in Anor Londo in Dark Souls.
How to fight Dark Sun Gwyndolin
To get to the hidden boss, Dark Sun Gwyndolin, first ensure that you do not want to join the Blades of the Darkmoon Covenant. From there you will want to ensure that you have the Darkmoon Seance Ring from The Catacombs and have it equipped.
From there, you will want to warp to Anor Londo. Here, you want to head to the lift and rotate it counter-clockwise and head down the spiral staircase towards a statue of Gwyn, lighting the bonfire along the way. Then, if you have the ring equipped properly, you should be able to head down a flight of stairs.
Then, you will hear a voice speak out to you. Kneel if you wish to join the Blades of the Darkmoon, or head through the Fog Gate to face Dark Sun Gwyndolin.
How to fight Dark Sun Gwyndolin boss strategy
Ensure that you have your weapons upgraded to their maximum, and equip some decent Magic Defense armour, as Gwyndolin is going to like to hurl that at you. Additionally, if you have occult weapons, you will be able to do a little bit of extra damage. Head through the fog door.
Immediately upon entering, you will find yourself in an infinite hallway, with Gwyndolin at the end. To your left and right are pillars, which you will be able to hide behind to heal or start your ranged assault, which is a viable strategy here. Gwyndolin has a few tricks up their sleeve while you're exposed in the hallway, which we're going to break down.
The first of their attacks is a sustained arrow assault, this will likely throw you off balance if you do not have a high stability shield or high poise, so what you will need to do is run in a zig-zag motion and go full serpentine, if you want to dodge these attacks and close distance on Gwyndolin.
Another of Gwyndolin's attacks is a homing Soul Spear, which is unblockable and incredibly fast. What we recommend doing as they cast this is to ensure that you run immediately to the left or right and ensure that you do not get stuck in any corners on your approach. The benefit to this is that you will be able to close distance enough to start doing melee damage on this boss.
The last attack in Gwyndolin's limited moveset is the homing Soul Arrows, which are incredibly difficult to run through, so ensure that you are defending or take cover when this spell is being cast.
Gwyndolin has some decent attacks to get you as you proceed through the corridor, so you might want to rush through some of these attacks as you get the hang of their patterns.
If you're looking for more help, our Dark Souls walkthrough and guide can help with all other areas of the game, including the dreadedTaurus Demon, Capra Demon, Ornstein and Smough bosses. Meanwhile, we have explainers on how to access DLC Artorias of the Abyss, the best gift and best class in Dark Souls, Dark Souls' best weapons, Dark Souls Covenants, Dark Souls Estus Flasks locations, Dark Souls Titanite Slab locations and NPC quests including Lautrec of Carim.
Finally, Gwyndolin will teleport as you get close, and then repeat those three attacks in different sequences. The most potent combination is the homing Soul Arrows, followed by the charged Soul Spear, which can kill you very quickly if you do not take cover as quickly as you can.
Then, you just want to deal as much damage as you can in quick succession in order to take this boss down, as they do not have much health at all, getting to the boss if you are a melee build is the hardest part of this.
After killing Gwyndolin, head down and towards the tomb, the chest on the right has the Brass armour set, and the chest in the middle holds a miracle.