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My kids finished my 5e conversion of Expedition to the Barrier Peaks on Saturday and the climax of the adventure was a battle against a CR 20 Illithid Space Marine.  Of course two level 12 characters have no chance against a CR 20 creature so they roused a squad of Sisters of Battle from stasis who were more than happy to  send said xenos back to hell.

You maybe thinking you don’t remember any of these details in the original S3.  Thats because the original adventure had no story.  I essentially play the adventure as is but layer a story over the top which has been refined over the years.  Now with the Iron Gods Adventure Path I ended up integrating the adventure and story into that storyline.  Will share the entire conversion and story at a later date.

One thing to remember when you look at the mind flayer that he has many “warp dependent” tagged abilities which essentially make it invulnerable to all damage on top of being an epic monster.  The build-up story allows the characters to disable the psycharious worm halo artefact which provides these benefits.

The battle lasted 5 rounds and the mind flayer managed to use his mind-blast 4 times.  In real time the battle took about 2 hours.  I included a shot of the battle map at the end.

Finally, mind flayer + space marine = awesome (for the DM) and terrifying (for the PCs)

Illithid Space Marine
Medium Aberration, lawful evil

Armour Class 20 (flayer battle-suit, Psycharius Worm)
Hit Points 405 (27d8 + 189)
Speed 30 ft., 40 ft in battle-suit

STR 27 (+8)                DEX 10 (+0)               CON 25 (+7)
INT 27 (+8)                WIS 15 (+2)                CHA 17 (+3)

Saving Throws Dex +6, Con +13, Int +13
Skills History +9, Perception +14, Persuasion +10, Stealth +6
Damage Immunities psychic, piercing, bludgeoning and slashing
Senses blindsight 60 ft., darkvision 120ft., passive Perception 24
Languages Aklo, Common
Challenge 20 (25,000 XP)

Legendary Resistance (3/Day). If Xallitharid fails a saving throw, it can choose to succeed instead.

Mind Flayer Paragon. Xallitharid has maximised hit points.

Magic Resistance. Xallitharid has advantage on saving throws against magical effects.

Magic Weapons. Xallitharid’s weapons are magical.

Psionic Celerity. Xallitharid has five initiative counts and acts five times per combat round. He may re-roll to recharge his mind blast per initiative count though it can only use mind blast once per round. He losses one count for every 100 hit points of damage.

Read Thoughts. The mind flayer chooses a creature it can see within 30 feet of it and attempts to read its mind. The chosen creature must succeed on a DC 13 Wisdom saving throw. Failed Save: The mind flayer can read the target’s surface thoughts for 1 minute. During that minute, the mind flayer also has advantage on Charisma (Deception) checks made to deceive the target and Wisdom (Insight) checks made to sense the target’s intentions.

Sense Thoughts. The mind flayer becomes aware of the presence of creatures within 100 feet of it that have an Intelligence score of 5 or higher.

Telepathy. The mind flayer can communicate telepathically with any creature within 200 feet of it that can understand a language.

The Psycharius Worm. Appearing like a tarnished brass maggot some six inches in length when dormant, the worm is cold and greasy to the touch and on first inspection appears to be nothing more than a macabre curio. However, when linked to the warp it possesses a terrible intelligence and provides multiple benefits to Xallitharid as an Illithid artifact. However, it has a weakness. Many of the traits it imparts are warp dependent. If cut-off from the warp Xallitharid loses all traits marked as “warp dependent”.

  • Psychofeedback. The Worm empowers the illithid’s strength grannie a +8 bonus (included).
  • Inertial Armour. The Worm provides an inky black carapace and provides physical protection to the illithid as a +2 to AC (included).
  • All Around Vision. The illithid is never surprised. This is a warp dependent ability.
  • Uncanny Dodge (1/day). As the shield spell. This is a warp dependent ability.
  • Breath of Life. Provides protection from the harshness of the Dark Tapestry as a void suit.
  • Empower Psyker abilities. Add +1 to psionic recharge abilities. The worm allows psionic abilities to be used more often. This includes mind blast for Xallitharid. This is a warp dependent ability.
  • Crimson Shield. Immune to all physical attacks. This is a warp dependent ability. Immunities become resistances if the worm is disabled.
  • Tower of ID. Immune to psychic damage. This is a warp dependent ability. Immunities become resistances if the worm is disabled.
  • Warp Puppets. Xallitharid targets one corpse of a humanoid or a Large or smaller creature within 20 feet of it and animates it with the power of the warp. In 1 minute, the corpse rises as a warp puppet. The corpse stays animated for 1d4 + 1 weeks or until destroyed, and it can’t be animated again in this way. Xallitharid usually as a coterie of warp puppets protecting his cabin. For game purposes these are identical to zombies but are immune to psychic attacks and flicker with a purplish glow. This is a warp dependent ability.

LEGENDARY ACTIONS                                  
Xallitharid 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. Xallitharid regains spent legendary actions at the start of his turn. These are all warp dependent abilities.

Beam Gun.  Xallitharid makes a Illithid Beam Gun attack.
Power Claw.  Xallitharid makes a Power Claw attack.
Body Adjustment (Costs 2 actions).  Xallitharid heals for 20 (4d8+4) damage.

Multiattack. Xallitharid can use its Unnerving Presence. It then makes three attacks: one with its tentacles and two with its beam gun or power claw. When available it may also use mind blast. It can also make an extract brain attack when opportunity arises.

Tentacles. Melee Weapon Attack: +14 to hit, reach 5 ft., one creature.
Hit: 18 (2d10 + 8) psychic damage. If the target is Medium or smaller, it is grappled (escape DC 18) and must succeed on a DC 18 Intelligence saving throw or be stunned until this grapple ends.

Power Claw. Melee Weapon Attack:+ 14 to hit, reach 10ft., one target.
Hit: 17 (2d8 + 8) slashing and 4 (1d8) force damage.

Illithid Beam Gun. Ranged Weapon Attack: +6 to hit, reach 200ft., one target.
Hit: 21 (3d6 +8) psychic damage.

Extract Brain. Melee Weapon Attack: +14 to hit, reach 5 ft., one incapacitated humanoid grappled by the mind flayer.
Hit: The target takes 55 (10d10) piercing damage. If this damage reduces the target to 0 hit points, the mind flayer kills the target by extracting and devouring its brain.

Mind Blast (Recharge 5-6). Xallitharid emits psychic energy in a 60-foot cone. Each creature in that area must succeed on a DC 18 Intelligence saving throw or take 64 (16d6 +8) psychic damage and be stunned for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Unnerving Presence. Each creature of the Xallitharid’s choice that is within 120 feet of it and aware of it must succeed on a DC 18 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature’s saving throw is successful or the effect ends for it, the creature is immune to Xallitharid’s Unnerving Presence for the next 24 hours.

Illithid Beam Gun (these glossy black rifles emit a ray of crackling purple lightning which tears open solid mass), The Psycharius Worm (artefact, intelligent, psionic, lawful evil).

This Xenos race appears have a humanoid body with an octopus-like head. They are a powerful psyker race. They have scattered colonies through out the Koronus Expanse and have had limited interaction with the Imperium – all of it violent.

Blonde bugbear = mind flayer, gray figures = sister of battle, pointy mini = Deathtrap, black characters = actual PC.   It made sense at the time!
Blonde bugbear = mind flayer, gray figures = sister of battle, pointy mini = Deathtrap, black characters = actual PC.  Dungeon map = bridge of the ship… It made sense at the time!
Posted in 5e, Dungeons & Dragons, Expedition to the Barrier Peaks


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  3. CG C

    Hey, I have to ask: how did you make your grid for spell spheres with that red wire? I’m trying to figure something out that’s not just paper. Any help would be appreciated, thanks.

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