Bosses

There are five bosses in the base game and one that is available through the Tower of Sisyphus as part of the Ascension DLC. Each boss has three distinct phases, which are indicated by orange pips above their health bar. Each phase has its own, full health bar as well as a unique set of actions and attack patterns which build upon previous phases. A boss is defeated when its third health bar is fully depleted.
After defeating them once, Phrike, Ixion, and Hyperion do not have to be defeated again in future cycles in order to clear their respective and continue to connecting areas. This significantly speeds up the process of getting to later areas within an act (i.e. getting to the Derelict Citadel from the Overgrown Ruins). Nemesis, Ophion, and Algos cannot be bypassed and must always be defeated to continue forward.

### Boss 1: Phrike

The first boss, Phrike, is encountered at the end of the Overgrown Ruins. They are vaguely humanoid, with three arms and a single eye. Their basic attacks consist of homing projectiles that must be strafed away from, dense fields of energy projectiles to dodge, and a shoulder charge in phases 2 and 3, which is indicated by them raising two of their arms back before moving to the player's position and striking. For new players with early equipment loadouts, Phrike is a challenging foe who requires patience and precise timing to overcome. Defeating them rewards the player with the Crimson Key.

#### Phase 1

Phrike keeps some distance from the player, firing projectiles, energy waves and laser beams from above, and tracking energy bolts. They also teleport occasionally, which is indicated by moving blue lights and a glowing red circle on the ground.

#### Phase 2

Phrike gets more aggressive, starting to use their shoulder charge and attacking more frequently. They gain the ability to create a pulse on the ground that damages players which is always followed up by a shoulder charge. The laser beam attack can now be used in a sweeping motion from left to right

#### Phase 3

Phrike gets much more aggressive, using their shoulder charge MUCH more frequently and chaining multiple attacks together in rapid succession. When sweeping their laser beam from left to right, they may now pause at the end of the sweep and send the beam back to the left, catching unaware players off-guard. Phrike's ground pulse attack now also creates a second pulse inside the first.

### Boss 2: Ixion

Ixion is encountered at the top of the Crimson Wastes. They have two ragged wings, a tentacle arm, and a blade-arm lodged in their chest. They focus on area control and denial, repeatedly forcing the player into tight spaces by flying around the arena and barraging the player with orbs and energy waves. Defeating Ixion rewards the player with the Icarian Grapnel.

#### Phase 1

Similarly to Phrike, Ixion will keep their distance during the first phase. They will fly across the arena, launch a series of orb attacks, then fly to a new position and repeat. While moving across the arena, Ixion will leave a trail of falling orbs that can be easily avoided.

#### Phase 2

At the start of the second phase, Ixion will land, the cloth around their head partially torn open, then fly up into the air. They will land again in the center of the arena, creating an energy wave as they raise their tentacle arm to the sky and roar. The environment will gain a light blue hue as Ixion starts rapidly firing energy waves (which have to be jumped over or dashed through), blue orbs on the ground, and blue orb bursts all around them for a moderate duration. After this ends, Ixion will become more aggressive and start using dive attacks (which are predated with a bird-like screech and consist of a wider orb-cone and an energy wave) and blue orb waves. Ixion also starts firing laser beams which are followed up with a large wave of tracking projectiles.

#### Phase 3

At the start of the third phase, Ixion, the cloth around their head completely torn open and revealing a bright yellow interior, will fly up into the air and back down again, causing their wings to lose their feathers, removing Ixion's ability to fly. They will then perform the same opening attack as in phase 2 with the addition of firing blue orb waves from their tentacle arm. Ixion then, with much effort and a scream, will remove the blade-arm from their chest and uses it as a weapon. From this point on, Ixion's attacks completely change. Instead of being distant like before, they will now leap and dash towards Selene, aggressively swinging their blade-arm, creating red projectiles with each slam and energy waves with each slash. One attack has Ixion slam the blade-arm into the ground, creating short-ranged projectiles and long-ranged energy waves with each slam. Ixion now also holds out their tentacle arm and fires two bursts of projectiles, one red and one blue. The blue projectiles are fired more rapidly and travel faster than the red ones. Ixion can now also teleport from side-to-side, creating a wave of red projectiles in front of them.

### Boss 3: Nemesis

Nemesis is encountered at the end of the Derelict Citadel. They are a monolith with a blue-flame face, floating turrets, and a glowing red core, which is the only point vulnerable to damage. They are arguably the hardest boss in the game (possibly tied with Ixion) and have some of the most drastic phase shifts of any of the bosses. As the phases progress, the player will need to perform some deft platforming in order to defeat Nemesis.

#### Phase 1

Nemesis fights the player on a single, large platform. The floating turrets will shoot laser beams while Nemesis launches blue orb waves for area denial and purple trackers and orange orbs to rapidly deal directed damage.

#### Phase 2

Phase 2 can have one of two modes: either the main platform will split into three medium-sized platforms with small platforms bridging them, or the main platform will remain but lose the raised barriers on its edges that prevent players from easily falling off.
In the first mode, Nemesis will appear at one of the three platforms. Players must be quick to move to the same platform as Nemesis, as the floating turrets will set the player's starting platform on fire relatively soon after the phase begins. From time to time, Nemesis will despawn and move to another platform, and the player should continue to follow them as quickly as they can, using the grapple points on the platforms for rapid movement.
In the second mode, Nemesis will appear at one end of the platform. The player should remain in the center of the platform to start, as the floating turrets will set about a third of the platform on fire starting from one of the edges, keeping the center safe. Nemesis will occasionally despawn and move to a different edge of the platform, and they player should again move to the center of the platform until the floating turrets pick an edge to light on fire.
Nemesis and their turrets' attack patterns are otherwise very similar to phase 1. Nemesis can now launch their purple trackers and orange orb simultaneously, and the floating turrets will now create two red rings instead of one during their attack.

#### Phase 3

All of the platforms from phase 2 will crumble, and Nemesis will send the player flying backward. Small platforms will start continuously dropping from the top of the screen, which must be grappled to in series to get close enough to Nemesis to start landing attacks. Something important to note is that Nemesis can send the player flying back more than once, so they should avoid getting right up against the boss, just stay close enough to deal damage. Nemesis now also rapidly fires wide, tall blue orb waves and can fire multiple waves of purple trackers at once. The floating turrets can now "snipe" the player after a duration, or can fire a red beam that destroys the platform the player is currently on.

### Boss 4: Hyperion

Hyperion is the fourth boss of Returnal and is found at the top of the spire in the Overgrown Ruins. The build-up to the boss involves Selene climbing the spire, with Hyperion's music growing louder and louder in the process. When Selene lands in the arena, Hyperion plays the "Don't Fear The Reaper" motif one last time before attacking. This boss is a humanoid-plant figure with a human head, a back shaped like an alien face, and vines connected to a nearby alien organ. This boss is obsessed with playing this organ, occasionally using it to deal damage throughout the fight while playing the boss's theme song, which is based off of Blue Oyster Cult's "Don't Fear The Reaper" (the song that was playing when Selene's crash occurred). Unlike the previous bosses in the game, Hyperion is entirely immobile while playing the organ, but can be fairly mobile when fighting the Selene head-on. In all phases, at 25% health, Hyperion focuses on playing the organ, causing various attacks to spew from the organ pipes. Something important to note is that it is possible to see what types of organ attacks Hyperion will use and where they go, but they require looking up farther and keeping an eye on the projectiles that come out of the organ pipes. In all phases, upon reaching 25% health, it is recommended to whittle Hyperion's health down quickly, as the right combination of projectiles from the organ can make damage extremely hard to avoid. At the end, Hyperion drops the Fractured Key for the Fractured Wastes.

#### Phase 1

Hyperion solely plays the organ, while firing out attacks at the player, from laser beam sweeps to dense projectile waves. If the player gets too close to Hyperion, they create thorns around themselves that damage the player. Around 25% health, they focus more on playing the organ, causing it to rapidly fire out various attacks (blue trackers, random green orb spread, tall orange orb waves) from the organ pipes.

#### Phase 2

Hyperion momentarily rips himself away from the organ, tearing one of the vines off, to fight the player head-on. They fire blue trackers, blue tracker waves, green orbs, a burst of two blue orb waves back-to-back, and waves of orange orbs at ground level. They can also create a wave of orange orbs in the air, which is followed by spawning tentacle pools at the player's feet, which will immobilize on hit until the player gets free. When they reach 25% health, they promptly go back to the organ to continue playing, resulting in the organ projectiles firing out once more, with the addition of the left and right sides of the arena being constantly barraged with red orbs (the barrage only occurs if the player goes over to the left and right sides) and the organ occasionally creating orange orb waves at the ground which spread out across the arena.

#### Phase 3

Hyperion, enraged, tears the other vine off, leaving them fully detached from the organ to more aggressively fight the player. Hyperion can do a ground slam, creating thorns and an orange orb wave around them, following by launching a blue orb "X" at the player. Hyperion also creates a field of blue orbs above the entire arena before "bringing the sky down." Hyperion can even create thorn lanes around the player before forcing them to dodge a series of orange orb pillars followed by green orbs on the floor. Hyperion can also create a ground pulse and leads their attacks more. Just like in the second phase, when they reach 25% health, they go back to the organ to play it one last time before being silenced forever.

### Boss 5: Ophion

Ophion is the fifth and final boss in the base game of Returnal and is found at the bottom of the Abyssal Scar. Ophion rapidly changes forms throughout the fight, but still keeps the same mechanic with each phase. Unlike other bosses, Ophion requires the use of the Delphic Visor to reveal nodes on the boss's body that have to be hit to deal damage. Ophion is entirely immobile and has widespread, visually spectacular attacks focused on area denial. Despite the appearance of these attacks, good dodging and keeping an eye on the Delphic nodes will help take this boss down fairly easily.

#### Phase 1

Ophion has a masked face, two three-fingered reed-like hands, and attacks with projectiles, beams, and kelp-like tentacles that slam the ground.

#### Phase 2

Ophion transforms to have the the appearance of an aged human skull and two three-fingered hands more shaped like human hands. Ophion also starts using a single-hand slam, a double-hand slam, and a hand sweep (the latter of which spans a large portion of the area) during this phase.

#### Phase 3

Ophion transforms once more, the boss's face becoming a shattered astronaut helmet with a skull barely visible, and the hands still have three-fingers, but being more tentacle-like in nature. Ophion starts using an attack that summons portals which, after a pause, fire a beam at the player's last location.

### Boss 6: Algos

Algos is the flesh-like monolith boss that can be found in the Tower of Sisyphus. It has a human-like skeleton in the center, which moves when enacting attacks, and a large purple eye at the top. Unlike previous bosses, fights against Algos do not initially include all three phases, instead adding phases as the player gets farther up the tower. Algos can only be damaged in its purple eye and has attacks that are extremely difficult to dodge, focusing on area denial and aggressively tracking Selene (two notable examples are the various flesh turrets it can summon around itself that fire squares full of purple projectiles, and the orange tracking beam it fires at Selene, which aggressively tracks Selene's current location and requires good dodge timing). Exercising extreme caution is advised for Algos, as, while Disruptors and high-damage sources can make short work of the boss, it is very much capable of making short work of Selene as well.

#### Phase 1

Algos is more distant, but still aggressive in its attacks. It fires purple orb barrages (both random and rectangular-shaped), a yellow orb attack that flies across the floor, a yellow beam attack that leaves a yellow orb wave in its wake, a quad orange orb beam attack that aggressively tracks the player's current location, an attack where it fires purple orbs into the sky that fall onto the player after a short time, and a single orange beam.

#### Phase 2

Algos gains fleshy spider legs and becomes more aggressive. Its starts to use fleshy turrets that circle around it, blocking attacks and firing purple orb barrages. Keep good movement to keep dodging attacks.

#### Phase 3

Algos uses its fleshy spider legs and tears the sides of its head open, creating the appearance of bat ears. Algos now also creates trackers, energy waves, and an orange orb wall that flattens out across the arena. Fleshy turrets are also created and fire much faster. Attacks in this phase are rapid and unrelenting. Killing the boss quickly in this phase is strongly encouraged.