Homebrew Deep Illithid Species Details

A forgotten colony of slavers, now enslaved by an entity far stronger. Having dug too deep down an ocean trench, the Mind Flayers encountered a Fathomless being, who destroyed their Elder Brain with ease and began using the inhabitants of the Far Realm as its personal minions. Over the course of eons, they've mutated and evolved into a completely different kind of Mind Flayer, much more suited to the deepest darkest abyss of the ocean floor. As the Fathomless beast moulds the colony to his liking, their bodies transformed, becoming even more squid-like. Abandoning humanoid legs and arms for tentacled appendages, they now swim at incredible speeds, breathe underwater, and use their psionic power to levitate whenever they have to traverse the surface world. With their feeding tentacles now replaced with appendages, Deep Mind Flayers feed with their arms instead of their 'mouths'.

They reproduce far slower and in much less numbers, since the process required to abduct hosts and bringing them to the bottom of the ocean floor for feeding and reproduction is much harder than taking them to a cavern deep in the Underdark. Without an Elder Brain's brine pool to gestate tadpoles, Deep Illithids used a completely different form form of reproduction with a different breed of tadpoles. Using a humanoid female's womb as a gestation chamber, a tadpole will take 10 months instead of 10 years to nature, after which they immediately Ceremorphosize their 'mother' hosts. Thus, all Deep Illithids use female humanoids as host bodies. As the generations of Illithids continued, they began to look more and more humanoid, adopting the appearances of their hosts. If a creature were to observe the Deep Illithid in the present, the would see them as a group of heavily mutated women, more in common with cephalopods than Mind Flayers.

Age. Deep Illithids mature the instant Ceremorphosis is complete, which is usually 10 months after a tadpole has gestated, and live up to 125 years. Their outward appearance is based on the age of their host's body.

Alignment. As with most Mind Flayers, Deep Illithids typically lean towards Lawful Evil, obeying the commands of their Fathomless overlord. 

Size. Barely humanoid, with over half their bodies being tentacles, Deep Illithids are even thinner than their regular counterpart. Your size is Medium.

Speed. Without legs to walk with, Deep Illithids use their innate psychic power to hover and fly around. You have a base flying speed of 20 feet, and a base swimming speed of 40 feet.

Languages. You can speak Deep Speech and Undercommon.

Deep Illithid Traits

As an aquatic variant of the Mind Flayers, Deep Illithids share many of the same traits, with a few notable differences.

Aberrant Mind

You have disadvantage on all Charisma ability checks in which you are not proficient. Your creature type is both humanoid and aberration.

Superior Darkvision

You can see in dim light within 120 feet of you as if it were bright light, and in darkness as if it were dim light. You can't discern color in darkness, only shades of gray.

Devour Brain

When a living creature you kill within 5 feet of you is reduced to 0 hit points, you can, as a reaction, devour their brain completely gaining temporary hit points equal to your level + your proficiency bonus.

This creature must have a size of Medium or smaller. Alternatively, as an action, you may consume the brain of a creature that has died within the last minute and gain the same benefits. You regain use of this trait once you complete a long rest.

Mind Blast

You can use your action to emit a psionic blast in a 15-foot cone. When you use your mind blast, each creature in the area of the blast must make a Intelligence saving throw. The DC for this saving throw equals 8 + your Intelligence modifier + your proficiency bonus. A creature takes 2d6 psychic damage on a failed save, and half as much damage on a successful one. The damage increases to 3d6 at 6th level, 4d6 at 11th level, and 5d6 at 16th level. After you use your mind blast, you can’t use it again until you complete a short or long rest.

Fathomless Blessing

You have a base swimming speed of 40 feet and can breathe underwater.

Ability Score Increase

Your Charisma score increases by 2, and your Intelligence score increases by 1.