The Old Demon King is an optional boss you can fight in Dark Souls III. He’s found deep beneath the Catacombs of Carthus, in the Smouldering Lake. Before picking a fight with him, I highly recommend putting on some armor with both fire and physical resistance, but be sure to prioritize your fire defense.
During the first phase of the fight, the Old Demon King will swing the large club in a wide arc in front of him. It’s a fairly easy move to out-range or roll through, so do whatever you’re more comfortable with. He’ll also perform a leaping strike, and you can roll forward to avoid it. This should put you in a good spot to get in a couple of hits on his legs. However, don’t get too greedy and make sure you have enough stamina to roll away. The Old Demon King usually follows up with a fire breath attack that can hurt you pretty badly if you don’t have the right armor on.
Once you’ve gotten him down to 50% health, he’ll get even more fiery with his attacks. When you see him thump his club on the ground slowly, get ready to roll because he’ll be summoning a ring of fire that closes in on the arena from behind. Once the ring of fire is right upon you, dodge backwards to avoid damage. The Old Demon King also has another AoE attack where he summons fireballs from the sky that home in on you. The good news is, he’ll be vulnerable to attacks while he’s summoning the fireballs, so it’s a great idea to get some hits in here. Keep your camera trained on the sky, and once you see the fireballs falling, start rolling around to dodge them. They’re fairly slow, so dodging them shouldn’t be much of a problem.
His fire breath attack in this second phase also has a ton of reach, and I advise rolling through the flames, especially if you don’t have a good fire-resistant shield. If you need to create distance between yourself and the boss so you can heal, you can always run away and take cover behind the large structures in the arena. While the fire breath attack can pass through obstacles, you should be safe from most of the Old Demon King’s other attacks.
The hardest part of this fight is surviving the boss’s attacks. While he’s pretty slow, his club can deal a massive amount of damage to you, and if you’re close to him, it’s very easy to get stuck on his feet while you’re trying to roll away, and this can usually lead to death. This is another fight where I’d advise taking things slow, and only go in for hits when you’re absolutely sure it’s safe. And if you do happen to get hit, immediately take cover behind the structures to heal up.
Be sure to check out our Dark Souls III wiki for more tips and tricks.