The three reported optional-boss locations in End of Abyss are the drained Reactor Pool, the upper Ventilation Tunnels, and Infirmary B1. Each requires a different unlock route: drain the pool for the Centipede rematch, open the tunnel route for the Brood Keeper, and unlock the Infirmary for the Morgue Dweller. Guides use “Husk Centipede” or “Centipede Husk” for the encounter; “Severed Husk Centipede” is another name used for it.
Optional boss locations at a glance
| Encounter | Location | Main access requirement | Reported reward |
|---|---|---|---|
| Centipede rematch (“Husk Centipede” or “Centipede Husk” in guides) | Drained Reactor Pool | Complete the Waterworks B3 drain sequence, then return to the Reactor | Vault Key #6, according to the guides |
| Brood Keeper | Upper Ventilation Tunnels | Enter from Factory East; use an Explosive Charge, Ventilation Maintenance Key, Grappling Hook, and switch | Vault Key #7, according to the guides |
| Morgue Dweller | Infirmary B1 | Unlock the Infirmary from the Lower Levels, then obtain a Restricted Access Keycard inside | Vault Key #8, according to the guides |
The locations and route details below are reported by third-party guides, not confirmed by a developer or publisher source. The guides describe these as the three additional Vault Key sources that complete an eight-key set.
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Where to find the Centipede rematch
Drain the Reactor Pool through Waterworks B3
The rematch takes place in the Reactor Pool after it has been drained. The reported sequence is in Waterworks B3:
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- Use the Grappling Hook to reach and operate a wall switch.
- Activate the switch near the circular structure.
- Operate the east-side pump console.
- Use an Explosive Charge to clear the blocked wall.
- Follow the upper-right route to reach the final switch and complete the drain sequence.
Return to the Reactor
Once the pool is drained, go back to the Reactor and climb down into the pool to trigger the encounter. Guides call this a Centipede rematch; the name varies between “Husk Centipede” and “Centipede Husk.”
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Where to find the Brood Keeper
Get the Ventilation Maintenance Key
Enter the Ventilation Tunnels from Factory East. Use an Explosive Charge on the weak wall near the easternmost entrance, then follow the route from F2 to F3. An ambush guards the Ventilation Maintenance Key there.
Open the upper-tunnel route
- Return to the lower-left part of F3.
- Use the Grappling Hook to lower a ladder.
- Use the Ventilation Maintenance Key to open the door and activate the switch.
- Return to F1 and climb the ladder in the circular room to reach the upper Ventilation Tunnels and the Brood Keeper.
Where to find the Morgue Dweller
Unlock the Infirmary
In the Lower Levels, burn a Parasitic Spire with the Incinerator to obtain the Infirmary Key. Then take the lift near the Habitation Sector shuttle to enter the Infirmary.
Reach Infirmary B1
On F1, collect a Restricted Access Keycard and use it to open the route down to B1. The Morgue Dweller is on the right side of B1.
Which route should you take first?
The guides do not establish a recommended order or compare the encounters’ difficulty. Choose based on which area and traversal tools you already have access to:
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- Reactor Pool: take this route if you can complete the Waterworks B3 drain sequence and have the Grappling Hook and an Explosive Charge.
- Brood Keeper: take this route if Factory East and the Ventilation Tunnels are accessible, and you can obtain the Maintenance Key and operate the required traversal route.
- Morgue Dweller: take this route if you can reach the Lower Levels, use the Incinerator on a Parasitic Spire, and secure the Infirmary keycard.
These route details and the Vault Key numbers are reported by third-party guides; no primary developer or publisher confirmation for the locations, sequence, or rewards is established here.
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