How to beat final boss Emperor Calus
Emperor Calus, the final boss of Destiny 2's Leviathan raid, is a difficult, exhilarating mix of everything the Leviathan has to offer. Calus is located through the 'cup' door in the Castellum. He's tough to bring down, but the loot and satisfaction is worth it, so let's go over how to “grow fat from strength.”
You of course find Calus in his throne room, but the fight actually takes place in two locations. You damage Calus and fend off his guards in the throne room, but you expose his weak points from within his 'Mind's Eye,' a shadowy dimension containing a giant version of his fat head.
At the start of each round, Calus will teleport your entire team into his Mind's Eye. Three players will return to the throne room, but three will remain to build up stacks of the 'force of will' buff, which increases the damage Calus takes. The players who leave must kill specific enemies in the throne room to protect the players who remain in the Mind's Eye. Once they've built up enough stacks, everyone groups up in the throne room and—surprise!—shoots Calus a bunch. Your goal is quite simply to kill him.
The initial wave
Start the fight by shooting Calus' pimp cup out of his hands, then clear the enemies that spawn. Once everything is dead, four 'psion councillors' will spawn on the plates in the throne room. Group up by one of the plates (it's best to pre-agree which one) and kill the councillor so you all get power ammo—but only one, otherwise more enemies will spawn in the throne room later.
Inside Mind's Eye
Shortly after the councillors spawn, Calus will clap his hands and teleport you into his Mind's Eye. Inside is a tiled 'runway' with a low barrier and three void orbs near the start. Three players, who you've pre-designated as the 'home' team, must jump over the barrier and use these orbs to return to the throne room. You don't have much time to reach the orbs, so be sure to designate who's grabbing which orb. We'll get to the home team in a bit. For now, let's focus on the three players who remain—the 'eye' team.
Every member of the eye team will see different symbols appear on Calus' giant forehead. These symbols correspond to the four plates in the throne room (dog, cup, plate and axe) and must be called out. Try to space your calls in a preset order so as to avoid overlapping and creating confusion. The point of these callouts is to alert the players in the throne room which psion councillor they need to kill, because one will have spawned on each of the four plates. Once the eye team calls out their three symbols, the home team must punch the psion on the plate whose symbol has not been called.
Let's say the eye team calls out dog, cup and axe. A member of the home team would then melee kill the psion on the sun plate. This will create a new barrier in Calus' Mind's Eye further along the runway, allowing the eye team to move up and preventing them from being sucked up by Calus.
On top of calling out symbols, the eye team must also deal with psions inside the Mind's Eye. Shortly after a set of symbols appear, three regular psions will spawn in the middle of the runway. You must kill them as quickly as possible, otherwise they'll use their knock-up grenades to bounce you over the barrier and into Calus' gaping maw. At the same time, two 'psion projections' will spawn to the sides of the runway. Kill these after the normal psions, but still quickly, to prevent a wipe.
On top of that, the eye team has to avoid the slanted tiles in the runway that can launch them over their barriers. Additionally, as Calus' health gets lower, more and more tiles fall away, creating holes which must also be avoided.
There's a lot going on in the Mind's Eye: The team must call out the symbols, shoot the psions, shoot the projections, avoid holes in the runaway and the ramped tiles. To simplify things and prevent players talking over each other, determine the order the eye team will call out their symbols, and have the person calling last declare which psion to kill. To go back to our previous example, the person who called axe would also call out "kill sun."
Once the eye team reaches the end of the runway, Calus' giant head will begin vomiting skulls. The more skulls you shoot, the more buff stacks you'll generate and the more damage you'll deal to Calus in the next phase. Auto rifles are ideal for killing these skulls. As always, have Titans use quick-reload Rally Barricades and have Warlocks use Arc Soul Rifts to add to the assault.
Once skulls stop spawning, four orbs will spawn at the end of the runway. The eye team must use these to return to the throne room and group up for the damage phase. Again, call out who will be using what orb to prevent confusion.
Outside Mind's Eye
While all that's happening inside the Mind's Eye, the home team will be fending off waves of Cabal in the throne room. Make especially good use of your supers, because you'll want to save power ammo for damaging Calus. Notably, the shields on the Cabal will change every round. They'll have void shields in the first wave, but arc and solar shields in future waves. Additionally, once Calus' health is low, flying centurions will be mixed into the waves. Just keep shooting. Improve your survival rate by staying toward the back of the throne room—as far from Calus as reasonably possible. Use the pillars to break line of sight on Calus' laser and funnel enemies down the sides of the room.
Of course, the home team's biggest job is killing the correct psions. To that end, it's useful to memorize the plate locations. Sun is in the back right, dog is in the front right, axe is in the front left, and cup is in the back left. A great way to distribute yourselves is to have one player handle the left plates, one player handle the right, and the other player guard the middle. This creates redundancy with all four psions, ensuring there's always someone available to punch the correct one.
Once the eye team begins shooting skulls in the Mind's Eye, the real Calus will start charging a team wipe in the throne room. To stop this wipe, the home team must break his shield, but not immediately. Skulls stop spawning once his shield is broken, which means fewer buff stacks. So, bring his shield very low and wait until the eye team has built about 40 or 50 stacks before breaking it. Skulls will continue to spawn for a short period after it's broken.
There are a few other tricks to this shield wipe. While it's charging, Calus will also deal DoT to the home team. Standing in a Warlock's healing Rift helps a lot, but if that Warlock is a Stormcaller, the Arc Souls the Rift provides may prematurely kill the shield. To keep things simple, group up behind the sun plate in the back right. Get Calus' shield to 20 percent, wait for the screen effect indicating the wipe is near, then break his shield. The exotic auto rifle Coldheart excels at this. It helps to have one player keep track of the shield damage and then call out 'push through' when it's time to break the shield. This player should also call out when to stop shooting the shield, to allow for maximum buff stacks. Again, be careful if you're using Arc Souls; they'll practically break the shield on their own.
When you break his shield, Calus will summon a large AoE where the home team is standing. This is a one-hit kill and must be dodged before the damage phase can begin.
You've called your symbols, punched your councillors and shot your skulls. Time to damage Calus. Have everyone group up near the sun plate in the throne room then jump onto it. You have to be on a psion plate to damage Calus, but each plate only stays active for so long once you step on it. So, be careful not to step on any other plates on your way to the sun plate.
Start on sun and work clockwise around. You'll know when to move when Calus raises his right arm. This animation signals the aforementioned large AoE, which Calus will fire at the current plate. If you don't get away in time, you will be one-shot, so keep an eye on Calus' movements. Do not wait for another teammate to call out this animation, and do not try to squeeze in a little more damage. You should call it out, but everyone should also be watching for Calus' right arm to move at all times. Staying alive is much more important than an extra couple of seconds of DPS.
In the first segment of his health bar, Calus' head will be his crit spot. In his second and third phases, it shifts to his chest. Coldheart and Merciless offer top-tier DPS for this fight. Once again, have Warlocks throw down Arc Soul Rifts, and if you have multiple Warlocks some of these should be set to empowering. Titans can use Rally Barricades for instant reloads, and Hunters should use Golden Gun with the Celestial Nighthawk exotic helmet if they have it. Everyone should also throw DoT grenades like pulse and voidwall. Sniper rifles and linear fusion rifles are also strong, as well as cluster bomb rockets. With average stacks (ie 50+) and decent damage output, you should be able to 'kill' Calus in three or fewer Mind's Eye cycles.
When Calus is out of health, he will begin charging his team wipe one last time. Stay on your current plate and lay into him. His final shield is durable, so you might want to save some power ammo for this phase. Break his shield one last time and you'll have defeated the emperor himself. Jump through the well in the middle of the throne room for some sweet loot and a big surprise.
It's also time to use those strange keys you've been collecting and crack open some hidden chests! You'll find more on that in our guide on the Leviathan's underbelly.