Arthrathag, The Coalesced

Devil's Sight. Magical darkness doesn't impede Arthrathag's darkvision.

Magic Resistance. Arthrathag has advantage on saving throws against spells and other magical effects.

Legendary Resistance (5/Day). If Arthrathag fails a saving throw, it can choose to succeed instead.

Spellcasting. Arthrathag casts one of the following spells, requiring no spell components and using Intelligence as the spellcasting ability (spell save DC 23) spellcasting modifier +10:

• Cantrip (at will) Firebolt

• 3rd level (1) Dispel Magic, Counterspell

• 4th level (3) Banishment, Polymorph

• 5th level (4) Hold Monster, Telekinesis, Dominate Person

• 6th level (3) Circle of Death, Disintegrate

• 7th level (4) Forcecage, Finger of Death*, Teleport*

• 8th level (4) Maze, Feeblemind

• 9th level (3) Meteor Swarm

Eye of Vecna. 

• You have truesight.
• You can use an action to see as if you were wearing a ring of X-ray vision. You can end this effect as a bonus action.
• The eye has 8 charges. You can use an action and expend 1 or more charges to cast one of the following spells (save DC 18) from it: clairvoyance (2 charges), crown of madness (1 charge), disintegrate (4 charges), dominate monster (5 charges), or eyebite (4 charges). The eye regains 1d4 + 4 expended charges daily at dawn. Each time you cast a spell from the eye, there is a 5 percent chance that Vecna tears your soul from your body, devours it, and then takes control of the body like a puppet. If that happens, you become an NPC under the DM’s control.

Hand of Vecna.

• Your Strength score becomes 20, unless it is already 20 or higher.
• Any melee spell attack you make with the hand, and any melee weapon attack made with a weapon held by it, deals an extra 2d8 cold damage on a hit.
• The hand has 8 charges. You can use an action and expend 1 or more charges to cast one of the following spells (save DC 18) from it: finger of death (5 charges), sleep (1 charge), slow (2 charges), or teleport (3 charges). The hand regains 1d4 + 4 expended charges daily at dawn. Each time you cast a spell from the hand, it casts the suggestion spell on you (save DC 18), demanding that you commit an evil act. The hand might have a specific act in mind or leave it up to you.

Eye and Hand of Vecna.

• You are immune to disease and poison.
• Using the eye’s X-ray vision never causes you to suffer exhaustion.
• You experience premonitions of danger and, unless you are incapacitated, can’t be surprised.
• If you start your turn with at least 1 hit point, you regain 1d10 hit points.
• If a creature has a skeleton, you can attempt to turn its bones to jelly with a touch of the Hand of Vecna. You can do so by using an action to make a melee attack against a creature you can reach, using your choice of your melee attack bonus for weapons or spells. On a hit, the target must succeed on a DC 18 Constitution saving throw or drop to 0 hit points.
• You can use an action to cast wish. This property can’t be used again until 30 days have passed.

Multiattack. Arthrathag makes four attacks with its chains.

Chain. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 23 (4d6 + 9) slashing damage. The target is grappled (escape DC 20) if Arthrathag isn't already grappling a creature. Until this grapple ends, the target is restrained and takes 14 (4d6) piercing damage at the start of each of its turns.

Animate Chains (Recharge 5-6). Up to four chains Arthrathag can see within 60 feet of it magically sprout razor-­edged barbs and animate under Arthrathag's control, provided that the chains aren't being worn or carried.

Each animated chain is an object with AC 20, 20 hit points, resistance to piercing damage, and immunity to psychic and thunder damage. When Arthrathag uses multiattack on its turn, it can use each animated chain to make one additional chain attack. An animated chain can grapple one creature of its own but can't make attacks while grappling. An animated chain reverts to its inanimate state if reduced to 0 hit points or if Arthrathag is incapacitated or dies.

Arthrathag can take 5 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. Arthrathag regains spent legendary actions at the start of its turn.

Chain Whip. Arthrathag makes one Chain attack.

Cantrip. Arthrathag casts one Cantrip.

Join The Coagulated Mass (2 Actions). Arthrathag attempts to engulf a creature within 5 ft. of him into the Coagulated mass. The target must make a DC 20 Dexterity saving throw or take 33 (6d10) points of necrotic damage. If a creature is reduced to 0 HP as a result of this damage, it begins to join the Coagulated Mass. Nothing can remove them from the Mass until the regain consciousness.

Coagulated Mass (3 Actions). Arthrathag polls the Solidified Clergy and removes one to use for his purposes. Make one action from the choices on the Solidified Clergy table.