Boss Guides

MIO: Memories in Orbit features 19 powerful boss battles throughout The Vessel: 6 story bosses and 13 optional bosses. 19 bosses total (6 story, 13 optional)—none are missable. These encounters test your combat skills, understanding of the Allocation Matrix system, and mastery of MIO's abilities.

Each boss has unique attack patterns and requires different strategies. Story bosses are required for progression, while optional bosses offer additional challenges and rewards.

Quick jump — Full boss list

Story:

Egis · Calderon · Sol & Vin · FLORA · Shii · Sawlong

Optional:

The Last Embedders · Dr Halyn's Collector · Twisted Baron · Dr Halyn's Experiment #223 · The Friends :) · Intrusive Fertiliser · Sentient Pearltrap · Terror of the Ledge

Story Bosses (6)

Egis

StoryTrophy: First Kill

First boss encountered in the game. Story-related boss that unlocks early progression.

Location: Early game area

Strategy Tips

  • Study attack patterns before committing to offense
  • Use your Hairpin Grapple to maintain mobility
  • Optimize your Allocation Matrix for combat abilities
  • Don't forget to use modifications that enhance your combat effectiveness

Calderon

Story

Defeating Calderon rewards you with the Old-Fashioned Key.

Location: Various areas of The Vessel

Strategy Tips

  • Study attack patterns before committing to offense
  • Use your Hairpin Grapple to maintain mobility
  • Optimize your Allocation Matrix for combat abilities
  • Don't forget to use modifications that enhance your combat effectiveness

Sol & Vin

Story

A dual boss encounter. After defeating them, climb to the top before the elevator and go right to find Lura's Seal.

Location: Specific area requiring progression

Strategy Tips

  • Study attack patterns before committing to offense
  • Use your Hairpin Grapple to maintain mobility
  • Optimize your Allocation Matrix for combat abilities
  • Don't forget to use modifications that enhance your combat effectiveness

FLORA

Story

Located before the Aviaries Passepartout. After defeating FLORA, go to the right to find this key item.

Location: Area leading to Aviaries

Strategy Tips

  • Study attack patterns before committing to offense
  • Use your Hairpin Grapple to maintain mobility
  • Optimize your Allocation Matrix for combat abilities
  • Don't forget to use modifications that enhance your combat effectiveness

Shii

Story

Secret final boss of the True Ending path. Fought in The Library (elevator third level), reached after completing The Crucible, obtaining Flowing Steps, and climbing the gloom waterfall in the Canopy.

Location: True Ending path - The Library (elevator third level)

Strategy Tips

  • Study attack patterns before committing to offense
  • Use your Hairpin Grapple to maintain mobility
  • Optimize your Allocation Matrix for combat abilities
  • Don't forget to use modifications that enhance your combat effectiveness

Sawlong

StoryTrophy: Aerial Maneuver

A chase boss encountered during a story sequence. You must grapple onto enemies without touching the ground to escape.

Location: Story chase sequence

Strategy Tips

  • Study attack patterns before committing to offense
  • Use your Hairpin Grapple to maintain mobility
  • Optimize your Allocation Matrix for combat abilities
  • Don't forget to use modifications that enhance your combat effectiveness

Optional Bosses (13)

Note: Optional bosses are not required for story completion but offer additional challenges, rewards, and trophies. Some are among the hardest encounters in the game.

The Last Embedders

OptionalTrophy: Shame On YouHardest

The hardest optional boss in the game. Found in the area way above Metropolis, accessible through the Dwellings.

Location: Area above Metropolis (via Dwellings)

The Last Embedders — How to reach & tips

How to reach: From Metropolis, head to the Dwellings (the region that connects to the area above Metropolis). Work your way through the Dwellings until you reach the arena above Metropolis where The Last Embedders awaits. For the full area layout, see our Maps & Exploration guide (Dwellings / Optional Areas).

Reward: Defeating The Last Embedders unlocks the "Shame On You" trophy.

Strategy: This is the hardest optional boss in the game. Consider tackling other optional bosses first to upgrade your loadout and modifiers. Use Corrupted Boss Mode in the Assist menu if you need a slight edge—bosses weaken after each death.

Why it's tough: The fight demands strong dodge timing and high damage output. Before attempting, grab more Coating Components and Mod Extensions for survivability, and equip combat-focused modifiers—see our Modifiers and Builds guides for boss-fight recommendations.

Strategy Tips

  • Study attack patterns before committing to offense
  • Use your Hairpin Grapple to maintain mobility
  • Optimize your Allocation Matrix for combat abilities
  • Consider using Corrupted Boss Mode if struggling (bosses weaken after each death)

Dr Halyn's Collector

OptionalTrophy: Rescued

Optional boss in the Vaults area. Found by going through the drawer in the large room, activating pumps, and jumping down the pipe at the end. Defeating this boss also saves Mel.

Location: Vaults area

Strategy Tips

  • Study attack patterns before committing to offense
  • Use your Hairpin Grapple to maintain mobility
  • Optimize your Allocation Matrix for combat abilities
  • Consider using Corrupted Boss Mode if struggling (bosses weaken after each death)

Twisted Baron

OptionalTrophy: Washing Machine

Optional boss found at the end of the Manufactory area. Requires finding all 6 Fragmented Serial Numbers to access.

Location: Manufactory area

Strategy Tips

  • Study attack patterns before committing to offense
  • Use your Hairpin Grapple to maintain mobility
  • Optimize your Allocation Matrix for combat abilities
  • Consider using Corrupted Boss Mode if struggling (bosses weaken after each death)

Dr Halyn's Experiment #223

OptionalTrophy: Maybe Knock Next Time?

Optional boss found in the Metropolis area. Located by dropping down a hidden hole on the stairs.

Location: Metropolis area

Strategy Tips

  • Study attack patterns before committing to offense
  • Use your Hairpin Grapple to maintain mobility
  • Optimize your Allocation Matrix for combat abilities
  • Consider using Corrupted Boss Mode if struggling (bosses weaken after each death)

The Friends :)

OptionalTrophy: A Web Of Lies

Optional boss found in the Canopy area. Requires obtaining the Friends Invitation from the room to the right, then opening the door at the bottom of the drop.

Location: Canopy area

Strategy Tips

  • Study attack patterns before committing to offense
  • Use your Hairpin Grapple to maintain mobility
  • Optimize your Allocation Matrix for combat abilities
  • Consider using Corrupted Boss Mode if struggling (bosses weaken after each death)

Intrusive Fertiliser

OptionalTrophy: Buried

Optional boss found by going down the gap to the right of the Promenade Entrance fast travel point.

Location: Promenade Entrance area

Strategy Tips

  • Study attack patterns before committing to offense
  • Use your Hairpin Grapple to maintain mobility
  • Optimize your Allocation Matrix for combat abilities
  • Consider using Corrupted Boss Mode if struggling (bosses weaken after each death)

Sentient Pearltrap

OptionalTrophy: Cutting the Weeds

Optional boss found in the Silo area.

Location: Silo area

Strategy Tips

  • Study attack patterns before committing to offense
  • Use your Hairpin Grapple to maintain mobility
  • Optimize your Allocation Matrix for combat abilities
  • Consider using Corrupted Boss Mode if struggling (bosses weaken after each death)

Terror of the Ledge

OptionalTrophy: Not This Time

A specific enemy found in the apartments area of the Nexus. Defeat it without taking a hit to earn the trophy.

Location: Nexus - Apartments area

⚠️ Must defeat without taking damage

Strategy Tips

  • Study attack patterns before committing to offense
  • Use your Hairpin Grapple to maintain mobility
  • Optimize your Allocation Matrix for combat abilities
  • Consider using Corrupted Boss Mode if struggling (bosses weaken after each death)

General Boss Strategy

Preparation

  • • Visit Network Gates before boss encounters
  • • Optimize your Allocation Matrix for combat
  • • Equip combat-focused modifications
  • • Consider sacrificing UI elements for more combat abilities
  • • Spend your Nacre before attempting difficult bosses

During Combat

  • • Learn attack patterns through observation
  • • Use Hairpin Grapple for positioning and evasion
  • • Chain grapple points to maintain momentum
  • • Look for safe windows to attack
  • • Don't be greedy—prioritize survival

Recommended Modifiers for Boss Fights

Your Allocation Matrix choices matter. For tough bosses, consider defensive modifiers (e.g. Protective Overlay for an extra health layer, Enhanced Dodge for better invincibility frames) and combat-focused modifiers for damage and mobility. Energy management helps—striking environmental objects restores energy so you can keep grappling and attacking.

  • • Defensive: Protective Overlay, Enhanced Dodge
  • • Offensive / mobility: Combat-focused modifiers that boost damage or movement
  • • Optional: Corrupted Boss Mode in the Assist menu weakens bosses after each death

For full lists and build ideas, see our Modifiers and Builds guides.

Boss Rewards

Defeating bosses rewards you with various items and progression:

  • •
    Key Items: Some bosses drop essential keys needed for progression (e.g., Old-Fashioned Key from Calderon)
  • •
    Nacre: All bosses drop Nacre, which can be used for upgrades
  • •
    Story Progression: Defeating certain bosses unlocks new areas and story content
  • •
    Abilities: Some bosses may unlock new traversal or combat abilities

Related Guides

ModifiersBuilds (Boss Fight Builds)Abilities & UpgradesEndings GuideCollectibles