Corpse Crawler (Imago)

Keen Smell. The corpse crawler has advantage on Wisdom (Perception) checks that rely on smell.

Spider Climb. The corpse crawler can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Light sensitivity. While in bright light, the corpse crawler has disadvantage on attack roles and Wisdom (Perception) checks that rely on sight.

Tunneler. The corpse crawler can burrow through solid rock at half its burrow speed and leaves a 10ft diameter tunnel in its wake.

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

Multiattack. The Corpse-Chewer makes three attacks: one with its tentacles and two with its bite.

Tentacles. Melee Weapon Attack: +8 to hit, reach 10 ft., one creature. Hit: 36 (8d6 + 8) poison damage, and the target must succeed on a DC 13 Constitution saving throw or be poisoned for 1 minute. Until this poison ends, the target is paralyzed. The target can repeat the saving throw at the end of each of its turns, ending the poison on itself on a success.

Bite. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 30 (4d10 + 8) piercing damage.

Acid Spit. Ranged Weapon Attack: +4 to hit, reach 30 ft., one target. Hit: 23 (6d6 + 2) acid damage.

Down, Down, Deeper n’ Down: Rock and earth spout into the air like water from a fountain as the Corpse Crawler surges downwards into the earth. The Corpse Crawler makes a move action, directly downwards. For the next turn, the Corpse Crawler cannot be attacked by any creature and may make no actions of its own. Then, it may re-emerge anywhere within 25 ft. of the point of its submergence.

Chosen of the Death God: The creature's inherent connection with death begins to ooze from it, seeping from the gaping wounds in its flesh. Anything bathed in this death-light begins to rot at the edges. After losing 50% of its hit points, the Corpse Crawler begins to exude a deathly aura. This deals 1d10 necrotic damage to any creature within 15 ft. of it at the start of its turn. This is a passive ability and occurs every turn after the Corpse Crawler is reduced to half-health.

Flesh Made Whole: The chitinous hide of the Corpse Crawler begins to ripple with bioluminescence, searing through the darkness. It seems to be restoring itself, somehow... Once per combat, the Corpse Crawler can heal itself as an action, drawing on the spirits of the dead it has consumed and knitting itself back together again. The Corpse Crawler restores 8d10 + 25 hit points. The Corpse Crawler may not take any other actions for the rest of the turn.

Devour: Flinging a player character into the air, the Corpse Crawler opens its throat, and ingests them in a single flex of its gullet. When the Corpse Crawler makes a successful bite attack on a creature, it can, as a bonus action, attempt to swallow them. If the target is a Large or smaller creature, it must succeed on a DC 18 Dexterity saving throw or be swallowed by the Corpse Crawler. A swallowed creature is Blinded and Restrained, has total cover against attacks and other Effects from outside the worm, and takes 2d10 acid damage at the start of each of the Corpse Crawler's turns. If the Corpse Crawler takes 28 damage or more on a single turn from a creature inside it, the worm must succeed on a DC 20 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 ft. of the worm. If the Corpse Crawler dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 20 ft. of Movement, exiting prone.

The Corpse Crawler 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 Crawler regains spent legendary actions at the start of its turn.

• Tunnel: The Corpse Crawler can make a move action, burrowing into the earth.
• Multiple attack: The Corpse Crawler makes a multiple attack.
• Acid Spit: The Corpse Crawler makes a an Acid Spit attack.

Your Death… Not Mine!: The Corpse Crawler furls itself, curling in upon itself into a ball like some vast, hideous woodlouse. Its armoured hide begins to striate with sickly, green light; a penumbra of magical energy crackles around it.

What: As an action, the Corpse Crawler can roll itself into a ball. It must remain like this for one full turn, during which it may take no other actions. While it is in this state, its AC increases by 5. All attacks made against the Corpse Crawler, whether melee, ranged, or magical, rebound upon the attacker.An attacker may make a DC 18 Dexterity saving throw to avoid being struck by their own weapons or projectiles, although doing so leaves them prone. Should they fail on this saving throw, they take the full damage from their spell, or weapon, as if the attack had been successful.

When: This is something the Corpse Crawler does early, especially if it is surrounded by martial characters, hitting it with big attacks, or if magic-users are starting to unveil their most damaging spells. It also requires the player characters to work out what's going on, and act accordingly. Never a bad lesson!

Makers Mark: Exploding through the floor, the Corpse Crawler's mouth splits along seams, yawning impossibly wide, and seeking to swallow everything in a single, vast bite!

What: Once per game, after submerging itself using the Down, Down, Deeper n' Down ability, the Corpse Crawler erupts through the floor, and makes a single bite attack within 5 ft of the Corpse Crawler. Any creature hit by that attack may attempt a DC 18 Dexterity saving throw or is devoured.

When: The Corpse Crawler uses this ability toward the centre of the fight, with the aim of breaking up the player character's plans entirely and taking at least one or two out of the fight for several turns. It's a devastating attack-and it should be!

Death Blow: As the Corpse Crawler writhes and undulates in its death-throes, its flesh begins to stretch and bulge, before erupting outwards in a hideous explosion of necrotic energy.

What: When the Corpse Crawler dies, it erupts, exploding outwards. Any creature within 30 ft. must succeed on a 18 DC Dexterity saving throw or suffer 3d10 necrotic damage.

When: As the ability says.. just as it dies. One does not kill something so heavily imbued with death and just walk away; you know?