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

Regeneration. The wriggling lord regains 20 hit points at the start of its turn if it has at least 1 hit point.

Return to Worms. When the wriggling lord is reduced to 0 hit points, it breaks apart into a swarm of insects in the same space. Unless the swarm is destroyed, the wriggling lord reforms from it 24 hours later.

Swarm Form. The wriggling lord can occupy another creature's space and vice versa, and the wriggling lord can move through any opening large enough for a Tiny insect.

Multiattack. The wriggling lord uses Dreadful Rot, Plague of Worms (if available), or Spellcasting. It then makes two Burrowing Lash attacks.

Burrowing Lash. Melee or Ranged Weapon Attack: +13 to hit, reach 10 ft. or range 120 ft., one target. Hit: 27 (6d6 + 6) piercing damage.

Dreadful Rot. The wriggling lord targets one creature it can see within 120 feet of itself, causing the target to decay from within. The target must make a DC 21 Constitution saving throw, taking 61 (7d8 + 30) necrotic damage on a failed save, or half as much damage on a successful one. A Humanoid killed by this damage rises as a zombie at the start of the wriggling lord's next turn and acts immediately after the wriggling lord in the initiative order. The zombie is under the wriggling lord's control.

Plague of Worms (Recharge 5–6). The wriggling lord conjures a torrent of worms in a 90-foot cone. Each creature in that area must succeed on a DC 21 Dexterity saving throw or take 22 (5d8) necrotic damage and be blinded and restrained by masses of swarming worms. The affected creature takes 22 (5d8) necrotic damage at the start of each of the wriggling lord’s turns. The creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If the affected creature starts the wriggling lord's turn with 0 hit points, it dies.

Spellcasting. The wriggling lord casts one of the following spells, requiring no material components and using Intelligence as the spellcasting ability (spell save DC 21):

At will: alter self, detect magic, detect thoughts, fireball, light, mage hand

2/day each: dimension door, fly, mislead, suggestion

1/day each: feeblemind, reverse gravity, time stop

Eldritch Shift. The wriggling lord teleports, along with any equipment it is wearing or carrying, to an unoccupied space it can see within 120 feet of itself. Alternatively, the wriggling lord teleports one creature it can see within 120 feet of itself, along with any equipment the target is wearing or carrying, to an unoccupied space within 120 feet of itself. An unwilling target must succeed on a DC 21 Charisma saving throw to avoid the effect.

Vile Counterspell. The wriggling lord interrupts a creature it can see within 60 feet of itself that is casting a spell. If the spell is 5th level or lower, it fails and has no effect. If the spell is 6th level or higher, the wriggling lord makes an Intelligence check (DC 10 plus the spell's level). On a successful check, the spell fails and has no effect. Whatever the spell's level, the caster takes 11 (2d10) psychic damage if the spell fails.