Gwyn, Lord of Cinder is the final boss of Dark Souls, coming after you explore Kiln of the First Flame.
How to prepare for Gwyn, Lord of Cinder
Ensure you are fully prepared to go into this fight, that means having your weapons fully upgraded, armour fully repaired and upgraded, have all the healing items you can possibly muster, summoning in any phantoms you might encounter, and finally making sure that you are happy with the build you are running going into the fight. Gwyn will give you almost no breathing room to heal or buff yourself, so be prepared for a pretty difficult fight here.
Gwyn, Lord of Cinder final boss strategy
Gwyn will immediately try to rush you down and hit you with a flurry of attacks with his flaming sword, which does Fire Damage in addition to Physical. We would actually recommend that you get a Black Knight Shield as a drop from one of the Black Knights outside of the Kiln to use in this fight, as it provides you with some pretty decent Fire Defense when going into the final boss battle.
While Gwyn will try to rush you down, we recommend that you get up close to him, this will cause him to strafe left and miss a lot of the attacks with his sword, leaving him relatively open to attack. From here, we would also recommend that you bait him for a backstab if he tried to grab you with his right hand.
The key to winning this fight is to simply observe Gwyn's hands. You will be able to discern what attack might be coming next just by looking at which way his hands are going. The hand to your left will be attacking with the sword, and the one to your right will be used for his deadly grab attacks.
The terrain of this fight does actually allow you for some respite along the way. The pillars in the boss room are good shields, where you may be able to have a window to heal. Don't do it unless you are completely certain, however, as the last thing you would want is a surprise rushdown by the final boss of the game.
There is also an additional way of beating Gwyn, remember that we talked about practicing your parry on those Black Knights in the Kiln?
Well, Gwyn so happens to be the only boss that can be parried, meaning that if you keep observing his hands like we said earlier, you should be able to time a parry and do some pretty decent damage to him if you have a good parrying window with a shield like the Heater Shield or Parrying Dagger. There are other options for parrying, we would just recommend sticking with one that you know.
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.
Additionally, if you find yourself struggling to defend against Gwyn's Attacks because it's draining your stamina, all you need to do is equip the Grass Crest Shield, which will help that Stamina recovery time a little bit so you might be able to recover from defending a little bit quicker.
Gwyn is not a hugely complex fight, it is relentless, and you will eventually learn every single pattern he has before killing him, simply because you will not have time to breathe during this fight, and it's also one that takes time to learn, so there is no shame in tackling this boss any way you want to- though we might not recommend rocking a bow the whole way through it.
Once you defeat Gwyn, you can either approach the bonfire or leave it to select your ending. Be warned, completing this fight will boot you into NG+ immediately, so if you've got other things to do before Gwyn, go do them!