Hold Breath. The Mindwyrm can hold its breath for 1 hour.

Multiple Heads. The Mindwyrm has six heads. While it has more than one head, the hydra has advantage on saving throws against being blinded, charmed, deafened, frightened, stunned, and knocked unconscious.

Whenever the Mindwyrm takes 40 or more damage in a single turn, one of its heads dies. If all its heads die, the Mindwyrm dies.

At the end of its turn, it grows two heads for each of its heads that died since its last turn, unless it has taken acid damage since its last turn. The Mindwyrm regains 15 hit points for each head regrown in this way.

Reactive Heads. For each head the Mindwyrm has beyond one, it gets an extra reaction that can be used only for opportunity attacks.

Wakeful. While the Mindwyrm sleeps, at least one of its heads is awake.

Enslave Minds. The Mindwyrm is capable of crushing the will of weak-minded creatures. The process takes 1 hour and only works on creatures with an intelligence score of 3 or less. Once a creature has been enslaved the Mindwyrm can command it directly. The enslaved creature gains Immunity to Charm and Frighten effects. 

If an enslaved creature dies while within 500ft of the Mindwyrm it takes psychic backlash, the Mindwyrm will take 20 points of psychic damage which bypasses its resistance. 

Multiattack. The Mindwyrm makes as many bite attacks as it has heads.

Bite. Melee Weapon Attack: +12 to hit, reach 15 ft., one target. Hit: 10 (2d8+7) piercing damage.

The Mindwyrm can psychically command an enslaved creature to make a single melee attack

The Mindwyrm can can take 3 legendary actions, choosing from the options below. It can take only one legendary action at a time and only at the end of another creature’s turn. The Mindwyrm regains spent legendary actions at the start of its turn.

Psychic Command (Costs 2 Actions). The Mindwyrm commands an enslaved creature to move up to half its speed and make a single melee attack

Compelled Will (Costs 2 Actions). The Mindwyrm gives an enslaved creature a new saving throw to end an ongoing effect caused by a failed Int, Wis, or Cha save. This new saving throw uses the Mindwyrm's save bonus.

Strangle The Mindwyrm tightens its grip on all creatures it has grappled. Each grappled creature takes d10+7 bludgeoning damage