Corpse Worm

Charge. If the Corpse Worm moves at least 20 feet straight toward a target and then hits it with a bite attack on the same turn, the target takes an extra 4 (1d8) bludgeoning damage. If the target is a creature, it must succeed on a DC 16 Strength saving throw or be knocked prone.

Legendary Resistance (3/Day). If the Corpse Worm fails a saving throw, it can choose to succeed instead.

Body Assimilation. Any creature with Organic Material reduced to 0 hit points Through a physical attack or when Swallowed must make a DC 12 Constitution save or be assimilated into the Corpse Worms body, the Corpse regains twice the creatures level or CR in hit points. The assimilated Creature takes an automatic death save fail each turn round unless the Corpse Worm is killed or the body removed.

Tunneler. The Corpse Worm can burrow through solid rock at half its burrow speed and leaves a 10-foot-diameter tunnel in its wake

Multiattack. The Corpse Worm makes two melee attacks. It can replace one of these attacks with one use of its Swallow or both for it's Vile Spit attack

Bite. Melee Weapon Attack: +10 to hit, reach 5 ft., one target. Hit: 12 (2d8 + 6) piercing damage. If the target is a creature, it is grappled (escape DC 14). Until this grapple ends, the target is restrained, and the Corpse Worm can't bite another target.

Swallow. The Corpse Worm makes one bite attack against a Medium or smaller creature it is grappling. If the attack hits, that creature takes the bite's damage and is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the Corpse Worm, and it takes 14 (4d6) acid damage at the start of each of the Corpse Worm turns.
If the Corpse Worm takes 30 damage or more on a single turn from a creature inside it, the Corpse Worm must succeed on a DC 15 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of the Corpse Worm. If the Corpse Worm dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 30 feet of movement, exiting prone.

Tail. Melee Weapon Attack: +10 to hit, reach 15 ft., one target. Hit: 11 (3d6 + 6) bludgeoning damage.

Vile Spit. Recharge 5 or 6. The Corpse worm spits out caustic poison in a  40 ft. cone all targets caught in the cone must make a DC 16 Dexterity saving throw, taking 11 (2d10) poison damage and 11 (2d10) acid damage, becoming poisoned for 1 minute on a failed save, or taking half as much damage and not becoming poisoned on a successful one. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

The Corpse Worm can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The Corpse Worm regains spent legendary actions at the start of its turn.

Attack. The eater of worlds makes one tail attack.
Move. The eater of worlds moves up to half its speed.
Chomp (Costs 2 Actions). The Corpse Worm makes one bite attack or uses its Swallow.

Call of The Grave. (cost 3 actions). The Corpse Worms inner red glow intensifies causing all living creatures in a 60 ft. radius to be filled with Dread experiencing visions of their death on a failed Wisdom save DC 15 and are Stunned until the end of their next turn. 

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