Menu Close


In “Dawn of the Overmind” after defeating the Unredeemed Beast the PCs make their way to the Overmind itself – a space station (or ethereal station) where the mind flayers are trying to undo reality and reinstitute their galaxy-wide empire. The PCs must use the Annulus to destroy the Engine Consumate (and thus the space station itself) to save their world and stop the mind flayers plans.  One problem, the engine is protected by Ilsensine’s avatar. And since the Annulus will take 10 rounds to work its magic they must hold of Ilsensine for the entire time.

With six well-prepared level 20 PCs I had no doubt they would be able to hold Ilsensine off.  In fact, I expected them to kill him. The “trick” was they had to do it in 10 rounds or they would go crazy due to his sanity draining presence. I also wanted to make the fight different so had a lot of reality-bending tricks going on – wiping spells from existence, swapping character sheets between characters etc.

My PCs called for divine intervention from the Raven Queen who reduced the time to 5 rounds instead of 10.  Another character had made a deal with derro godling Dinkanrazin to trade the ring of ilsensine to him if he helped fight Ilsensine – which he readily agreed to.

On the off chance, my PCs failed I had a backup plan. The starbase was under attack by a githyanki fleet of spelljammers and red dragons.  I was planning on having that battle play out with the PCs running the gith who are attempting to destroy the station. But it never came to that.  My PCs were victorious and the mind-flayers suffered a galaxy-shaking defeat.

The other thing I did was hand-wave the entire space-station exploration/avoid mind flayers part. It didn’t seem well developed and a group of epic-level characters are not going to have any issues with CR 7 mind flayers or CR 1/2 grimlocks that litter the space station.  

Control Nexus of the Engine Consummate

The double doors to the Engine Consummate bears a familiar face. – a relief carving of a gargantuan illithid with six tentacles – Ilsensine – extinguishing suns by grasping and smothering them with its tentacles alone.

When you open the doors the hum that fills this chamber is the quintessential boom, grading into depths of sound below which the ear cannot define, but from which an ominous vibration is born that pierces your body like light through glass. The sound fills the chambers that are otherwise almost bare of features and draw attention to the expanse of ebony that serves as the far wall. The wall’s subtle convex bulge suggest that it is but the barest part of a massive sphere that extends beyond the limits of this chamber. At the base of the “wall”, a single figure stands, gazing at some small panel affixed to the onyx surface, list in the majesty of the hum.

Once attacked or attacks: The creature drops to the floor with one hit and it moans and groans there as it swells in size. When its full avatar form comes upon it, Ilsensine‘s height is greater than 20 feet, its tentacles grow at least as long, and the nails on its four-fingered hands grow into menacing black claws. Its eyes glow like a beacon, and its mauve skin leaves a trail of purple radiance in the air marking its passage.

Ilsensine is happy to talk so long as the Annulus is not triggered. He compliments the party on their skill at solving his trials and thanks them for bringing the Annulus. He then asks for the Annulus indicating the high honour of them becoming his personal thralls – for as long as they live.

The Yellow Sign of Maanzacorin glows angrily in Ilsensines presence.

The changeling’s tentacles continue to secrete flesh-dissolving enzyme; however, the extreme size of the tentacles render them more akin to acid-soaked battering rams. Ilsensine loses its extract brain trait when fully revealed unless the target is also gargantuan.

Lowball. Hand the PC a card that says “lowball”. When a PC fails a saving throw turn card over, now low numbers are better than high for d20 rolls.

Insanity. Just being in the presence of Ilsensine causes all characters to lose a sanity point each round. Characters lost to insanity are effectively dead. Characters with a god listed on their character sheet never drop below 1 sanity point. It takes 10 rounds of uninterrupted concentration to trigger the Annulus.

Gargantuan aberration (mythic, mythos), lawful evil
Armor Class 21 (natural armor)
Hit Points 702 (36d20+324)
Speed 40 ft., fly 60 ft., swim 40 ft.

30 (+10) 13 (+1) 29 (+9) 30 (+10) 25 (+7) 30 (+10)

Saving Throws Str +19, Con +18, Int +19, Wis +16, Cha +19
Skills Arcana +15, Perception +16
Damage Immunities cold, poison, psychic*
Condition Immunities charmed, frightened, paralyzed, petrified, poisoned
Senses blindsight 60 ft., darkvision 60 ft., truesight 60 ft., passive Perception 26
Languages deep speech, telepathy 300 ft.
Challenge 30 (155,000 XP)
*Ilsensine is still affected by Maanzacorin’s Ultrablast.

Insanity. All non-aberrations within telepathic range of Ilsensine automatically lose 1 Sanity per round at the start of Ilsensine’s turn. Characters with deities written on their character sheet never drop below 1 sanity but now have a permanent bane on all d20 rolls. There is a price to pay when facing the mythos.

Maddening Resistance (1/Turn). If Ilsensine fails a saving throw, it can choose to succeed instead. The creature that forced Ilsensine to make the saving throw loses 1d2 Sanity.

Magic Resistance. Ilsensine has advantage on saving throws against spells and other magical effects.

Overwhelming Mind. Ilsensine’s mind is overwhelming in its power and alien structure. He is immune to any effect that would sense his emotions or read his thoughts, and divination spells. This even foil wish spells and spells or effects of similar power used to affect his mind or gain information. The first time a creature other than an aberration makes mental contact with Ilsensine, it must succeed at a DC 27 Wisdom saving throw or contract indefinite madness. On a successful save, the creature cannot take reactions and can make either an action or a bonus action (not both) for 1 round; creatures that are immune to being stunned are unaffected. This effect can occur whether Ilsensine initiates mental contact (such as via a dream, or once per round merely by telepathic communication) or another creature attempts to do so (such as via detect thoughts or dominate monster). Once a creature is exposed to Ilsensine’s overwhelming mind, it is immune to this effect for 24 hours.

Psionics. Ilsensine’s spellcasting ability is Intelligence (spell save DC 27). He can innately manifest any spell as a psionic power. This power is always cast at the maximum spell level.

Divine Discorporation. If Ilsensine is killed, his body immediately fades away into a noxious cloud of otherworldly vapour that fills an area out to his reach. This cloud blocks vision as fog cloud but can’t be dispersed by any amount of wind. Any creature in this area must succeed at a DC 26 Constitution save or be poisoned for as long as it remains in the cloud and for an additional 1d10 rounds after it leaves the area. Ilsensine returns to life after 2d6 rounds, manifesting from the cloud and restored to life via true resurrection, but for 2d6 rounds cannot take reactions and can take either an action or a bonus action on his turn but not both. If slain again while he is suffering from this effect, Ilsensine reverts to vapour form again and his essence fades away after 2d6 rounds, returning to The Caverns of Thought for a time.

Starflight. Ilsensine can survive in the void of outer space and flies through outer space at incredible speeds. Although the exact travel time will vary from one trip to the next, a trip within a solar system normally takes Ilsensine 2d6 hours, and a trip beyond normally takes 2d6 days (or more, at the GM’s discretion).

Multiattack. Ilsensine can use its Unspeakable Presence. He then makes six attacks: two with its claws and four with its tentacles. It can shove a creature in place of a claw attack.

Sweeping Claws. Melee Weapon Attack. +19 to hit, reach 40 ft., targets all creatures in a 10-foot square. Each claw attack drains a random spell (roll 1d10 -1 then select a spell randomly).
Hit: 19 (4d6 + 10) slashing damage. Make one attack roll; any creature in the area whose AC is equal to or lower than the result takes damage from the claw.

Tentacle. Melee Weapon Attack. +19 to hit, reach 40 ft., one target.
Hit: 21 (2d10 + 10) bludgeoning damage plus 9 (2d8) acid damage. If the target is a creature, it is grappled (escape DC 29). Until this grapple ends, the target is restrained. Ilsensine has four tentacles with which to grapple targets; while a tentacle is being used to grapple, it cannot be used to attack a different target.

Cognizance Explosion (Recharge 3-6). Ilsensine psionically manifests psychic energy in a 90-foot cone. Each creature in that area must succeed on a DC 27 Intelligence saving throw or take 101 (26d6 + 10) psychic damage and be stunned for 1 minute on a failed save, or half as much damage on a successful one and the target is not stunned. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Unspeakable Presence. Each non-aberration, non-fiend within 300 feet of Ilsensine and aware of him must succeed on a DC 27 Wisdom saving throw or become frightened for 1 minute. A creature that becomes frightened drops to 0 hit points and begins dying. A creature that is immune to being frightened and fails the saving throw becomes incapacitated for 1 minute; at the end of each of the target’s turns it may make a new saving throw, becoming no longer incapacitated on a success. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to Ilsensine’s Unspeakable Presence for the next 24 hours.

Non-Euclidean. Ilsensine does not exist wholly in the physical world, and space and time strains against his presence. He may add a +9 bonus to AC when an attack would hit or +9 to his Dexterity saving throw when he would fail. This can cause an attack to miss or Ilsensine to succeed at a saving throw.

Ilsensine can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. Ilsensine regains spent legendary actions at the start of his turn.

  • Claw Attack. Ilsensine makes a claw attack.
  • Esoteric Reality. Ilsensine imposes one of the following effects:
    • Wipe a spell from history. Pick a spell that the PCs commonly use. This spell no longer exists.
    • Swap characters. Randomly swap two PCs character sheets for the rest of the battle (minds have been swapped).
    • Randomize spells. When a spellcaster attempts to cast a spell make a Constitution saving throw equal to DC 10 + spell level. On a failure, the PC casts a random spell instead (roll 1d10-1 and then pick a random spell from that level).
  • Trample (Costs 2 Actions). Ilsensine moves his movement rate without provoking opportunity attacks. He may move through the spaces of other creatures of less than Gargantuan size, ending in an unoccupied space. Each creature whose space he passed through must succeed on a DC 27 Dexterity saving throw or take 19 (2d8 + 10) bludgeoning damage and be knocked prone.

Ilsensine’s Lair
Ilsensine’s lair is the Cavern of Thought. However, his presence has permeated the Overmind and it is considered his lair for this adventure.

Lair Actions
On initiative count 20 (losing all initiative ties), Ilsensine can use one of his lair action options. He can’t do so while incapacitated or otherwise unable to take actions. If surprised, he can’t use one until after his first turn in the combat.

  • Unnatural chill permeates a 20-foot radius centred on a point Ilsensine can see within 120 feet. Creatures in the area must succeed on a DC 15 Constitution saving throw or take 14 (4d6) cold damage.
  • Shadows of the mind afflict a 20-foot radius centred on a point Ilsensine can see within 120 feet. Creatures in the area must succeed on a DC 15 Wisdom saving throw or suffer a short-term madness.
  • Non-Euclidean Shifts. Ilsensine chooses two creatures within 120 feet that he can see. The targets must succeed on a DC 15 Intelligence saving throw. On a failure, the creature moves up to 10 feet in a direction of Ilsensine’s choice, without provoking opportunity attacks or causing the target to leave a solid surface or a body of water. If both targets fail, Ilsensine can instead switch their positions.

Regional Effects

  • Creatures that sleep within 1 mile of the lair can sense Ilsensine’s dreams. Dreamers may be inspired, frightened, or bewildered.
  • Ilsensine’s huge astral base seems to defy ordinary geometry. Passages and rooms may overlap or differ in length, seemingly in contradiction of physical possibility.
  • Intelligent creatures within 1 mile of the lair may gradually develop various forms of madness. The more sensitive or powerful the intellect, the worse the madness. These effects end within 1d10 hours of Ilsensine’s final defeat, as he slips into a death that is not death.
Posted in 5e, Dawn of the Overmind, Dungeons & Dragons

Leave a Reply