Multiattack

The nihileth makes two Tentacle attacks and one Tail attack, or it makes three Withering Touch attacks.

Tail (Undead Form Only)

Melee Weapon Attack: +10 to hit, reach 10 ft. one target. Hit: 15 (3d6 + 5) bludgeoning damage.

Tentacle (Undead Form Only)

Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 12 (2d6 + 5) bludgeoning damage, and the target must succeed on a DC 15 Constitution saving throw or contract the nihilethic rot disease (see the Nihilethic Rot trait).

Withering Touch (Void Ghost Form Only)

Melee Spell Attack: +9 to hit, reach 10 ft., one creature. Hit: 14 (3d6 + 4) necrotic damage.