Avatar of Lolth

Pride of the Spider Queen (Once/Short or Long Rest). When Lolth is reduced to 0 hit points, her current hit point total instead returns to 615, she recharges her Corrupted Divinity if it is on cooldown, and regains all Legendary Actions. Additionally, Lolth may now use the options in the "Mythic Actions" section of her stat sheet for 1 hour.

Legendary Resistance (5/day). If Lolth fails a saving throw, she may choose to succeed instead.

Magic Weapons. The Avatar of Lolth's weapon attacks are magical.

Shapechanger.  The Avatar of Lolth can use its action to polymorph into a form that resembles a female drow or giant spider, or back into its true form. Its statistics are the same in each form. Any equipment it is wearing or carrying is transformed. It reverts to its true form if it dies.

Mind of the Goddess. Lolth is immune to psychic damage, any effect that would sense her emotions or read her thoughts, divination spells, and the charmed condition. Mind of the Goddess even foils wish spells and spells or effects of similar power used to affect Lolth's mind or to gain information about the target.

Body of the Goddess. Lolth's stats can not be changed and she can not have her power siphoned away. She is also immune to disintegration and cannot have her form changed in any way.

Necrotic Aura. Any creature that starts their turn within 30 ft. of Lolth takes 2d10 necrotic damage. Any dying creature within 120ft of Lolth has disadvantage on death saving throws.

Spellcasting. Lolth is a 20th-level spellcaster. Her spellcasting ability is Widom (spell save DC27, +19 to hit with spell attacks). Lolth has the following spells prepared:

At will:  bane, bestow curse, blight, command, darkness, dispel magic, fear, misty step, shadow of moil, vortex warp

5/day: black tentacles, cloudkill, counterspell, divine word, immolation, mental prison

3/day: banishing smite, harm, circle of death, dominate monster, finger of death

1/day: antimagic field, psychic scream, meteor swarm, ravenous void

Multiattack. Lolth makes 6 attacks, using any combination of her sword, web, bite, and leg attacks. She may replace one attack with a use of her fling.

Vorpal Sword. Melee Weapon Attack: +22 to hit, reach 15 ft., 1 target. Hit: 39 (4d12 + 13) force damage. When Lolth attacks a creature that has at least one head and she rolls a 20 on the die for the attack roll, she cuts off one of the creature's heads. The creature dies if it can't survive without the lost head. A creature is immune to this effect if it is immune to slashing damage, doesn't have or need a head, has legendary actions, or the creature is too big for its head to be cut off with this weapon. Such a creature instead takes an extra 27 (6d8) slashing damage from the hit.

Web. Ranged Weapon Attack: +17 to hit, range 60/240 ft., 1 target. Hit: 22 (3d8 + 8) necrotic damage. A creature hit with this attack is restrained. A restrained creature may use an action to attempt a DC22 Str check to end this restraint. The webs may also be attacked. They have an AC of 18 and 20 HP.

Bite. Melee Weapon Attack: +19 to hit, reach 5 ft., 1 target. Hit: 28 (4d8 + 10) piercing damage and the target must make a DC26 Constitution save, taking 65 (10d12) poison damage and becoming poisoned on a failed save. While poisoned in this way, the creature takes 33 (5d12) poison damage at the start of each of their turns. On a success, the creature takes half damage and is not poisoned.

Impaling Leg Strike. Melee Weapon Attack: +19 to hit, reach 20 ft., 1 target. Hit 36 (4d12 + 10) piercing damage and the target is grappled (escape DC25). While grappled in this way, the creature is restrained. The avatar of Lolth may have up to 6 creatures grappled in this way at a time.

Fling. Lolth throws a Large or smaller creature she is grappling up to 200 feet away horizontally in a direction of Lolth's choice. The grapple ends for that creature, and it must make a DC 23 Dexterity saving throw. On a failed save, a creature takes damage as if it had fallen the distance it was thrown and falls prone. On a successful save, a creature takes half as much damage and isn't knocked prone.

Corrupted Divinity (Recharge 6). A wave of energy emanates from Lolth, carrying both corruptive and divine energies with it. Every creature within 90 ft. of Lolth must make a DC26 Constitution save, taking 84 (15d10) necrotic damage and 84 (15d10) radiant damage on a failed save.

Teleport. As an action, Lolth can teleport, along with any objects or creatures she is holding, to a location of her choice within 120 ft. 

Spider's Cunning. Lolth can dash, disengage, or hide as a bonus action.

Reactive. Lolth can take one reaction on every turn in combat.

Warcaster. The Avatar can cast a spell in place of a melee weapon attack when making an attack of opportunity. This spell must target a single creature.

Parry. When she is hit with a melee weapon attack, The Avatar may parry it, adding 6 to her AC.

Quick Footed. When a creature ends its turn within 15 ft. of Lolth, she can move up to half her movement speed. This movement does not provoke opportunity attacks.

The Avatar of Lolth has 5 legendary actions that she can use at the end of another creature's turn.

Vorpal Swing (Costs 1 action). Lolth makes an attack with her Vorpal Sword.

Crushing Legs (Costs 1 action). Lolth can force a creature she has grappled to make a DC23 Constitution save, taking 5d8 piercing damage on a fail.

Web Walker (Costs 1 action). Lolth can move up to her movement speed. This movement does not provoke opportunity attacks.

Spellslinger (Costs 3 actions). Lolth can cast any of her known spells.

If Lolth's Pride of the Spider Queen has been activated in the last hour, she can use the following options below as Legendary Actions.

Wrathful Embrace (Costs 2 actions). Lolth can use her Web attack, targeting up to 3 creatures within range.

The Fury of the Spider Queen (Costs 4 actions). Lolth can move up to double her movement speed, making a Vorpal Sword attack against each creature she moves within range of. At the end of this movement, she can make an Impaling Leg Strike attack and fling the grappled creature if it hits. This movement does not provoke opportunity attacks.