Unusual Nature Brain in a Jar doesn't require air, food, drink, or sleep.
Detect Sentience Brain in a Jar can sense the presence and location of any creature within 300 feet.
Magic Resistance. Brain in a Jar has advantage on saving throws against spells and other magical effects.
Multiattack. Brain in a Jar makes a Mind Blast and casts one spell each turn.
Mind Blast. The brain magically emits a psychic energy in a 60-foot cone. Each creature in that area must succeed on a DC 17 Intelligence saving throw or take (2d8+5) psychic damage and be stunned for 1 minute. A stunned creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
Innate Spellcasting. The Brain casts one of the following spells, requiring no material components and using Intelligence as the spellcasting ability (spell save DC 17):
At will: detect thoughts, mage hand, zone of truth, charm person, hold person, compulsion, hold monster, and sleep.
3/day each: dispel magic , fear , Tasha's hideous laughter
1/day: teleport
Chill Touch. Whenever the Brain is hit with a melee attack the attacker takes (3d8) necrotic damage, and the target can't regain hit points until the start of the Brain's next turn.