This resource features the general description of a location in the pseudo-physical manifestation of an elder brain’s oneiric collective. It includes adventure ideas that are appropriate for high-level (Levels 12 to15) adventuring parties. Challenge Rating (CR) is calculated using a party of four as the model.
The DM is free to change or modify any or all the information found here. NPC names and settlement names are the first the DM should consider changing to accommodate any homebrew world lore. To modify the challenge rating of the adventure, the DM must first consider the power level of the party. Considering the PCs’ individual levels and the number of players is crucial to presenting a good challenge. Not all parties are the same, different playing styles and command of the system in the party can increase or decrease their effectiveness in encounters. The DM may adjust the encounters slightly by adding or subtracting monsters. Alternatively, controlling monsters with more intelligence and strategy is often the easiest way to raise the difficulty of an encounter.
When monsters are referenced, book name and page numbers are noted in parenthesis. Be aware that page numbers may vary depending on the book print. If the DM can’t find a monster where noted, it means it is a different book print. Page differences tend to be small so whatever is missing will be reasonably close to the pages noted in the adventure.
Of all the terrors and abominations out there, only the ignorant will argue against the notion that illithids are the worst of all. Illithids, often referred to as mind flayers, are the overlords of the Underdark. They orchestrate plots that take centuries to happen. It is understood that illithids have been present in the material plane and some outer planes since the ancient past. There is also a record of illithids arguing that time is retrochronistic. Presenting arguing that is alleged to come from the far future, like the technology used in their plane-faring airships.
Illithids are individually extremely intelligent creatures. They surpass humans, elves, and other humanoid intelligent races by two orders of magnitude. Scheming against the illithids is playing a losing game. Illithids tend to be ten steps ahead. They are often impatient, waiting for things to pass that are inevitable but that they plotted years ago.
There is a darker truth behind it all. While informed people may believe that illithids are the master schemers behind the world’s’ woes. Most of the time, they are just pawns to a greater more powerful entity, the elder brain. The elder brain is the cornerstone of every mind flayer community. It is the central repository of knowledge, not only of its own community. But also of ancient illithid knowledge of the past and future. In the majority of illithid communities, illithids are as much mental thralls of the elder brain as actual thralls created by individual members. Illithids are certainly free roaming individuals within the community, as long as they comply with the elder brain’s commands. Should an illithid choose to refuse direct commands from the elder brain, it would have to fight the mental assault of the elder brain’s incredible mental power. There are some rogue illithids roaming alone in the world, but they are the exception to the norm. A rebellious illithid often becomes the elder brain’s food.
Illithids are the source of nightmares mainly because of their alien shape and their form of eating. The way they capture a living person and then destroy their skull to devour their brain is considered to worst way to go by adventurers. Not only is it a haunting demise, but most forms of resurrection magic are thwarted by the absence of the actual brain tissue. when a person is slain by an illithid, it often means a real end to that person’s story. This was not something that worried the extremely wealthy: kings, merchants, and powerful clergy are immune to most tragedies except old age.
This is a common misconception. People found out about this centuries ago when an important tribe leader was killed by an illithid. Being in his position, the tribe leader would have been resurrected by the most powerful healing magic available to them. Except that it did not work. It didn’t matter that the brain was missing, the magic could work around that. The real problem was that the soul was missing. At first, the clergy thought the leader did not want to return from the afterworld. That is something that can happen. But they were wrong. For some reason, the soul was missing. Further research revealed that people killed by illithids may also have their soul, their life force, absorbed in the process. Illithids are mentally connected to each other through a kind of neural meta-network that stays outside of the material world. All mental connections eventually converge to a single point, the elder brain. Some researchers call this convergence of consciousness the Illithid Oneiric Collective. At first glance, it appears to only be a network of minds connected to each other, but people discovered that it had a pseudo-physical representation. There is no way to explain it in simple terms but it exists outside everything, like its own plane. Yet, it is accessible by powerful mental creatures like illithids.
Scholars theorized that the missing souls were part of the elder brain’s collective consciousness. One of those scholars dared to propose that the souls may be retrievable if a person managed to access the Illithid Oneiric Collective. These propositions were discarded as nonsense by fellow peers. The current theory states that only upon destroying the elder brain would the souls be freed. The few scholars knowledgeable about this still disagree. It does not help that none of those things have ever happened, so it is all conjectures.
These facts have come back to living memories due to a recent tragedy. The king of a great nation was slain one full moon ago. The nobles at the court tried to keep it silent, expecting the high priest to perform a resurrection. It all failed. The king had been slain by a mind flayer and his soul was irretrievable. The news hit the kingdom bad. Everyone foresees a coup or a revolution soon. The young king did not have children yet, but his queen is currently pregnant. A famous scholar formulates that the illithids are trying to change the chain of succession. They might want the soon-to-be-born king to assume the throne immediately upon being born. Or the queen and that baby are in great danger.
The kingdom’s peace still remains walking on the edge of a knife. It needs but a push to drown the country in terror and war.
This is a high-level adventure idea that will most certainly need some adjustments before use. The DM should adjust the lore above to his or her own homeworld. That is why the dead king and the kingdom are not given names.
In high-level adventures (levels 11 to 15), it is possible for adventurers to have close relationships with kings and rulers. If the party already knows a king or other person of great power, it is appropriate to use that NPC for this adventure. The NPC would have to die to the illithid and be unable to be revived. This should not be permanent if the adventurers manage to retrieve his or her soul from the Illithid Oneiric Collective.
The Illithid Oneiric Collective is something similar to the ethereal plane. It exists outside of the material plane but it is only accessible mentally, like the dream realm. Adventurers may enter the Illithid Oneiric Collective if they kill an illithid and then prepare a delicate infusion with the creature’s brain. Upon drinking it, the adventurers fall to a semi-comatose state that lasts for as long as they need to complete the mission. During this time, their physical bodies appear to be sleeping and are vulnerable.
- Welcome Room
Adventurers arrive to the Illithid Oneiric Collective here. There is a table and chairs made of pulsating brain matter. Upon arriving, the adventurers might suffer a mental shock. The Illithid Oneiric Collective is a place so alien that it defies understanding. The DM is advised to use the Madness rules here.
- Breeding Room
There is a brainy pond full of purple-grey liquid. This room is used to breed 6 Intellect Devourers(MM, page 191). 2 Mind Flayers (MM, page 221) oversee the room.
- Room of Memories
This room provides access to all memories within the Illithid Oneiric Collective. That is the memories of currently connected illithids, the elder brain, and the souls of people trapped here. There is no way to establish direct communication or conversation with any of them, it’s just a repository of memories. Illithids can access any memory as if they searched for books in a library, but adventurers will have to make a DC 18 Arcana (Intelligence) check to retrieve any useful memories from the room. There are 2 Mind Flayer Arcanists (MM, page 221) in the room.
- Mental Surgery Room
Illithids use this room to bring people’s minds from the material world here for manipulation. There are four people tied to each of the purple “beds” in the room. These people, like the adventurers, are not really here, it is just their mental representation in the Illithid Oneiric Collective. There is an Arcanaloth (MM, page 313) named Dur’Yan here. He was invited to experiment and share some of his knowledge. There are also 2 Intellect Devourers (MM, page 191) and 1 Mind Flayer (MM, page 221) here.
- Abandoned Chamber
There is no apparent use for this abandoned chamber but adventurers will find it difficult to leave. Upon entering, the fleshy circular doors solidify and won’t reopen as usual. They will have to force their way through the bio-matter that surrounds them to any of the adjacent rooms.
- Dining Room
3 Mind Flayers (MM, page 221) are in the middle of consuming what appears to be humanoid sized brains that are set on a table made of the same material. The illithids attack the adventurers immediately.
Where is the King?
The Illithid Oneiric Collective holds the king’s soul in it, but it has to be taken by force and the guardian is the consciousness of the illithid elder brain. When the adventurers are exploring either Area 3 or Area 4, the DM should describe the physical transformation of one of the outer walls into a gigantic brain behind a glassy tank. This is not the actual elder brain but its mental representation in the Illithid Oneiric Collective. (The Elder Brain is found in Volo’s Guide to Monsters)
Defeating the elder brain here does not kill it, but it makes it sleep for a week. During this time the Illithid Oneiric Collective becomes unstable and all trapped minds find a way to escape. The adventurers will not be able to explore further after defeating it because the oneiric plane breaks down without the elder brains mental power keeping it together.
These are the general features of the illithid oneiric collective. The location exists outside of reality and can only be accessed by drinking an infusion of mind flayer brain to induce a semi-comatose state.
Terrain. The floor and walls are made of gray matter. They are firm but fleshy. Walls and floor pulsate to an unseen heart’s beat. Some blood vessels are visible through the floor in certain locations.
Doors. There are fleshy circular membranes in certain walls, they open automatically when a creature gets close to them. They are marked on the map with a symbol.
Light. There are no visible light sources but all chambers are brightly illuminated.
Smells and Sounds. The adventurer’s sense of taste is suppressed in the oneiric collective. It is replaced by the illithid’s equivalent which is a type of psychic-taste. Touching things like the walls or creatures leaves a mental after-taste which reveals surface thoughts similar to the Detect Thoughts spell. The only perceivable sound is that of blood flowing and a faraway thumping heartbeat.