The first boss in The Ringed City, the final DLC for Dark Souls 3, feels like it was designed to be a co-op battle. You face off against two giant flying demons, the Demon in Pain and the Demon from Below, and after taking those two out, one morphs into The Demon Prince for a final, prolonged showdown. But if you’re a stubborn Souls player and must finish everything on your own (and I understand), here’s what to keep in mind when taking on the final demons.
Phase one: The Twin Demons
The first phase is all about spatial awareness. One demon is always aggressive and glowing orange, coming at you with a few swiping and leaping attacks that are all telegraphed well ahead of time. Dodge-roll like you were born to. Just keep in mind that the other demon is hanging back and puking up toxic clouds this whole time and chances are, if you’re not paying enough attention, his toxic puke attacks will intersect with where you’re dodge-rolling. Their toxic attacks are also telegraphed with animations and sound and well ahead of time. Mostly, they’re meant to be a distraction from the aggressive demon coming your way. If you don’t trust yourself to keep track of that jerk in the back, equip some toxic-resist rings and bring plenty of Blooming Purple Moss Clumps, just in case.
From here, it’s a test of skill. By now, you should have your invincibility frame window for dodge-rolling down, so observe the aggressive demon’s fairly simple move set—he swipes and charges—and respond appropriately. Take a swing or two between attacks, back off, and observe again. As always, getting overzealous in Dark Souls will be the reason most folks die. With enough consecutive hits to the face, you can stun the big bats and go in for a critical hit that does a ton of damage and knocks them over for more.
At some point, the aggressive demon will exhaust their power, their orange glow will fade, and they’ll start puking toxic fumes too. When this happens, the other demon will light up shortly after, becoming orange and angry while their bro takes a breather. Swapping places doesn’t do much to change up the fight other than to encourage you to focus on whatever health bar has been depleted the most so far. If you think you can keep track of the aggressive demon while finishing off the toxic demon, go for it, but I’d just stick to whatever rhythm you’re most comfortable in. This fight can go on for a long, long time, as you’ll soon find out.
Phase two: The Demon Prince
Oh cool! A new life bar appears once you take out the two demons, a battle which is already as difficult as any from the main game. Now you need to kill The Demon Prince, who doesn’t behave very princely. This bigger, more fiery bat likes to fly and leap all around the arena, which makes him hard to keep up with. Even when he's vulnerable after a move for a hit or two, the prince is probably on the other side of the cavern. Distance shouldn’t be too much of an issue, so long as you learn to read the prince’s attacks to predict their position.
Meteor shower - When you get close, sometimes the prince looks up and wails, summoning a few molten boulders fall from the sky. They fall slowly and if you know they’re coming, just back off and strafe, but don’t run away. The prince will rest, giving you a short window to attack.
Divebomb - When the prince flies up, he’ll wind up and dive down, leaving a trail of fire in its wake. Dodge out of the way and sprint to where the prince lands. He rests for a second or two, leaving him open to attack.
Fire spheres - The prince will cup his hands and summon two balls of fire that spit smaller fireballs at you. He prince likes to leap backwards after summoning the balls, which pushes out a gust of air that can knock you on your bottom. Give chase, but don’t stand still and avoid approaching directly. Zig-zag, dodge roll a bit, and make your way to the prince, who will likely take a few swipes at you, leaving him open for a few hits of your own.
This GIF demonstrates what not to do.
Fireballs - If the prince cups one hand and summons a single fireball, he's about to hop into the air and toss it your way. Advice: don’t get hit. The sphere doesn’t move super fast, so don’t jump the gun on that dodge roll too soon.
The greatest challenge in this long fight is patience. The Demon Prince’s inflated health bar and inability to stand still means each attempt can take upwards of 10 minutes as you dip and dodge around every fire attack, chipping away all the while.
Still need help?
There's always something else to try:
You can summon the NPC Lapp on the ledge right before dropping into the arena.
You can also summon NPC Slave Knight Gael at the bonfire right before the arena.
Upgrade those weapons. Enemies in The Ringed City are Titanite pinatas.
Just summon some co-op friends. Praise the sun. What else is it there for?