Yagnoloth

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

Multiattack. The yagnoloth makes one Electrified Touch attack and one Massive Arm attack, or it makes one Massive Arm attack and uses Battlefield Cunning, if available, or Teleport.

Electrified Touch. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 27 (6d8) lightning damage.

Massive Arm. Melee Weapon Attack: +8 to hit, reach 15 ft., one target. Hit: 23 (3d12 + 4) force damage. If the target is a creature, it must succeed on a DC 16 Constitution saving throw or become stunned until the end of the yagnoloth's next turn.

Battlefield Cunning (Recharge 4–6). Up to two allied yugoloths within 60 feet of the yagnoloth that can hear it can use their reactions to make one melee attack each.

Life Leech. The yagnoloth touches one incapacitated creature within 15 feet of it. The target takes 36 (7d8 + 4) necrotic damage, and the yagnoloth gains temporary hit points equal to half the damage dealt. The target must succeed on a DC 16 Constitution saving throw, or its hit point maximum is reduced by an amount equal to half the necrotic damage taken. This reduction lasts until the target finishes a long rest, and the target dies if its hit point maximum is reduced to 0.

Spellcasting. The yagnoloth casts one of the following spells, requiring no material components and using Charisma as the spellcasting ability (spell save DC 16):

Teleport. The yagnoloth teleports, along with any equipment it is wearing or carrying, up to 60 feet to an unoccupied space it can see.