Crypt Worm

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

Grave or Crypt Rot. If afflicted by cryptworm rot, the victim cannot regain hit points unless a restoration spell or cure disease is cast upon them, and they take 4 points of necrotic damage per turn at the end of their turn. The loss of hit points caused by the necrotic damage becomes permanent if not cured within 10 minutes.

Multiattack. The worm makes two attacks: one with its tongue lash and one with its bite.

Bite. Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 22 (2d8 + 10) piercing damage. If the target must make a DC 16 CON save or take an additional  14 (4d6) necrotic damage. 

Tongue Lash. Melee Weapon Attack: 3-6 hooked tongues can launch from its mouth +10 to hit, reach 20 ft., multiple creature. Each Hit: 19 (2d4 + 4) piercing damage, and the target must make a DC 14 Dexterity saving throw, or be restrained. It must also make a DC13 CON save or contract cryptworm rot and becomes [Tooltip Not Found] . 

Vomit.  As a bonus action the crypt worm can vomit on a restrained creature, causing 3d6 acid damage and 3d6 necrotic damage. Pieces of half-consumed undead flesh pour out in a liquid soup, and the creature must make a DC12 CON save or suffer cryptworm rot.  The bonus action recharges on a 5 or 6 (1d6) at the start of its turn.

Frenzied Roll. As a reaction, when surrounded by foes (more than 1 in a 5 foot radius) and damaged the cryptworm can go into a frenzied roll causing Hit: 19 (4d8 + 4) crushing damage. DC 12 DEX save for half, and avoid being knocked prone.