Ur-Mind Illithid Druid

Magic Resistance. The mind flayer has advantage on saving throws against spells and other magical effects.

Innate Spellcasting (Psionics). The mind flayer’s innate spellcasting ability is Intelligence (spell save DC 15). It can innately cast the following spells, requiring no components:

At will: detect thoughts, levitate

1/day each: geas, plane shift (self only)

Aberrant Wildshape. The mind flayer magically polymorphs into an aberration form of CR 1 or lower or back into its original form. Any equipment is absorbed into the aberration form. It reverts to its normal form when it dies. It uses the aberration form's hit points and hit dice, and when it returns to its normal form it returns to the number of hit points it had before it transformed. While polymorphed, the mind flayer's statistics and abilities are those of the aberration form, except proficiencies, intelligence, wisdom, and charisma scores. The mind flayer may cast its innate psionic spells while polymorphed, but not its druid spells. The mind flayer may remain polymorphed for 6 hours at a time. (2x/day).

Fungal Infestation. The Mind Flayer's spores gain the ability to infest a corpse and animate it. If a beast or a humanoid that is Small or Medium dies within 10 feet of the mind flayer, it can use its reaction to animate it, causing it to stand up immediately with 1 hit point. The creature uses the zombie stat block in the Monster Manual. It remains animate for 1 hour, after which time it collapses and dies.

In combat, the zombie’s turn comes immediately after its creator. It obeys the mind flayer's mental commands, and the only action it can take is the Attack action, making one melee attack.

Spellcasting. The mind flayer is an 8th-level spellcaster. Its spellcasting ability is Wisdom (spell save DC 16, +8 to hit with spell attacks). It has the following druid spells prepared:

Cantrips (at will): druidcraft, frostbite, resistance, thorn whip, shillelagh 

1st level (4 slots): cure wounds, entangle, faerie fire 

2nd level (3 slots): flame blade, heat metal, pass without trace 

3rd level (3 slots): conjure animals,  (summons aberrations instead of beasts, though with the same CR restrictions), dispel magic, erupting earth   

4th level (2 slots): confusion, hallucinatory terrain 

Symbiotic Entity. The mind flayer can expend a use of Wild Shape to awaken its spores, rather than transforming into an aberration form, and gain 10 temporary hit points. While these temporary hit points remain, the mind flayer’s melee weapon attacks deal an extra 1d6 necrotic damage to any target they hit.

Tentacles. Melee Weapon Attack: +7 to hit, reach 5 ft., one creature. Hit: 15 (2d10 + 4) psychic damage. If the target is Medium or smaller, it is grappled (escape DC 15) and must succeed on a DC 15 Intelligence saving throw or be stunned until this grapple ends.

Extract Brain. Melee Weapon Attack: +7 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). The mind flayer magically emits psychic energy in a 60-foot cone. Each creature in that area must succeed on a DC 15 Intelligence saving throw or take 22 (4d8 + 4) 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.

Halo of Spores. The mind flayer is surrounded by invisible necrotic spores that are harmless until it unleashes them on a creature nearby. When a creature it can see moves into a space within 10 feet of the mind flayer or starts its turn there, the mind flayer can use its reaction to deal 1d6 necrotic damage to that creature unless it succeeds on a DC 16 Constitution saving throw.