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

Undead Fortitude. If damage reduces the Undead Mind Flayer Toddler Assassin to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the Undead Mind Flayer Toddler Assassin drops to 1 hit point instead

Immutable Form. The mind flayer toddler is immune to any spell or effect that would alter its form. It is essentially a flesh golem.

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: Dimension Door (50 ft, self only)

1/day each: Vampiric Touch, Blur

Drawn to Intelligence: The Mind Flayer Toddler Assassin is driven by two things; the assigned task and intelligence. In the absence of an assigned target to kill, it targets the highest intelligent creature determined by its Innate Spellcasting (Psionics). The target may make a DC15 intelligence save to avoid this. This action is considered a bonus action in combat.

Know your Enemy: The Undead Mind Flayer Toddler Assassin will observe its target outside of combat to learn its capabilities, including assessing intelligence without using psionics.

Multiattack: The mind flayer toddler makes two attacks. Either two attacks from its daggers, or one attack from its daggers and one from its tentacles.

Melee Attack: The Mind Flayer Toddler attempts to stab you to climb up your body to your head. Melee Weapon Attack. +7 to hit, Reach 5 ft. one creature.  Hit: 3 (1d4+2) piercing damage

Dimension Door Drop: One of the Undead Mind Flayer Toddler Assassin's favorite tactics is to open a dimension door 10 feet over a targets head to drop on them. This is a standard Melee Weapon Attack. +7 to hit, Reach 5 ft. one creature.  Hit: 3 (1d4+2) piercing damage and 4 (1d6) fall damage from the attack. If this attack hits, the target must make a Escape DC 15 check or be considered grappled . (The Mind Flayer Toddler has successfully landed on the targets face/head.)

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. This attack will heal the Undead Mind Flayer Toddler Assassin for 1/4 of damage dealt.

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. This attack will heal the Undead Mind Flayer Toddler Asssasin for half the damage dealt.

If the Undead Mind Flayer Toddler Assassin does not gain a surprise round, it will cry out psychically and summon 1d4+1 Swarm of Stirges which will target any living creature within range.

As a reaction, if the Mind Flayer Toddler Assassin drops below 1/4 health, it will cry out in angiush, unleashing a Mind Blast. 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. This affect may only happen once.

If the Undead Mind Flayer Toddler Assassin drops below half health it will instantly cry out psychically and summon 2d4+1 Swarm of Stirges which will instantly appear to close one the nearest three enemies.

If the Undead Mind Flayer Toddler Assassin drops below 3/4 health, it will being to utilize Dimension Door ability to escape.

If the Undead Mind Flayer Todller Assassin successfully executes Extract Brain, it automatically executes an additional Dimension Door Drop attack against an appropriate target.