Dreadful Aura. At the start of the conqueror worm's turn, every living creature that can see it must succeed on a DC 17 Wisdom saving throw or be frightened. A frightened creature can repeat the saving throw at the end of each turn, ending the frightened condition if successful. Celestials and fiends are immune to this trait.
Eternal. The conqueror worm cannot be permanently destroyed. Even if utterly annihilated, it will reform a year later in a place strongly connected with death, such a cemetary or battlefield.
Feed On Fear. As long as at least one creature within 50ft. of the conqueror worm has the frightened condition, the conqueror worm regenerates 20 hit points at the start of each of its turns.
Legendary Resistance (2/day). If the conqueror worm fails a saving throw, it can choose to succeed instead.
Material Plane Native. Despite being a fiend, the conqueror worm is considered a native of the prime material plane for the purposes of spells such as banishment.
Plague-Bringer. The conqueror worm is immune to disease.
Bite. Melee Weapon Attack: + 12 to hit, reach 10ft., one target. Hit: 20 (3d8+7) piercing damage, and the target must make a DC 19 Constitution saving throw. If the saving throw fails, the target is diseased. Every twenty-four hours, a diseased target loses a hit die and takes 10 necrotic damage. As long as the disease persists, neither hit die loss nor necrotic damage caused by it can be restored. A creature reduced to zero hit points from this damage dies. The disease is magical and cannot be cured by nonmagical treatment. Once the disease is cured, the necrotic damage heals normally, and lost hit dice return at a rate of one per long rest.
Constrict. Melee Weapon Attack: +12 to hit, reach 10ft., one Medium or smaller target. Hit: 21 (4d6+7) bludgeoning damage, and the target is grappled (escape DC 20). Until the grapple ends, the target is restrained, and the conqueror worm cannot constrict another target.
The conqueror worm can take three legendary actions, chosen from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. The conqueror worm regains spent legendary actions at the start of its turn.
Fast Bite. The conqueror worm makes a bite attack.
Squeeze. The conqueror worm does automatic 21 (4d6+7) bludgeoning damage to a creature it has in a grapple.
Slither. The conqueror worm moves up to its speed.
Description
The enormous bloated body of this worm-like creature is a sickly yellowish-white. Its head vaguely resembles that of an ant, with large fangs encrusted with the gore of former victims. Between its bulbous eyes is a black marking resembling a skull.
The conqueror worm was created by a god of death to be a constant reminder to mortals of the inevitability of their demise. Whenever the death god feels he hasn't been given his due, he sends the conqueror worm to slay and destroy. It enjoys using its bite to infect victims with a disease known as living death. The bodies of victims decompose as though they were corpses.
It is said that as long as mortals die, the conqueror worm cannot be destroyed. It will return again and again, as unstoppable as death itself. Some theologians claim that the conqueror worm is the death god's trump card. If death were irradicated, then the conqueror worm would perish, reintroducing death to the world.