Aries the Arachno-Lich

Legendary Resistance (8/Day). If the Arachno-Lich fails a saving throw, it can choose to succeed instead.

Rejuvenation. If it has a phylactery, the destroyed Arachno-Lich gains a new body in 1d10 days, regaining all its hit points and becoming active again. The new body appears within 5 feet of the phylactery.

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

Web Sense. While in contact with a web, the Arachno-Lich knows the exact location of any other creature in contact with the same web.

Web Walker. The Arachno-Lich ignores movement restrictions caused by webbing.

Multiattack. The Arachno-Lich makes eight attacks.

Meteoric Slam. Melee AoE Attack: +9 to hit. Hit: 17 (8d6) Bludgeoning damage, and the target must succeed on a DC 20 Strength saving throw or be prone. Those within 5 feet of the landing site can make a DC 15 Dex save to avoid the damage.

Venomous Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., one creature. Hit: 17 (5d6) poison damage, and the target must succeed on a DC 20 Constitution saving throw or be poisoned for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Wither. Ranged Spell Attack: +9 to hit, range 60 ft., one target. Hit: 14 (4d6) necrotic damage.

Fire Storm (7th-Level Spell; 1/Day). The Arachno-Lich fills up to ten 10-foot cubes with fire. Every cube must be within 150 feet of the lich and occupy a space the lich can see, and each cube must have at least one face adjacent to the face of another cube. Each creature in the area must make a DC 20 Dexterity saving throw, taking 38 (7d10) fire damage on a failed save, or half as much damage on a successful one. The fire ignites flammable objects in the area that aren’t being worn or carried. If the lich chooses, plant life in the area is unaffected by the spell.

Spellcasting. The Arachno-Lich casts one of the following spells using Wisdom as the spellcasting ability (save DC 19):

At will: druidcraft, Poison Spray

3/day each: detect magic, fog cloud, pass without trace 

1/day each: antilife shell, dispel magic, speak with plants, transport via plants

Magi-Web (Recharge 5–6). Ranged Weapon Attack: +8 to hit, range 30/60 ft., one creature. Hit: The target is restrained by webbing. As an action, the restrained target can make a DC 20 Strength check, bursting the webbing on a success. The webbing can also be attacked and destroyed (AC 10; hp 8; vulnerability to lightning damage; immunity to bludgeoning, poison, and psychic damage).

The Arachno-Lich can take 8 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 Arachno-Lich regains spent legendary actions at the start of its turn.

Attack. The Arachno-Lich makes an attack.

Poison Prick (Cost 2 Actions). The Arachno-Lich targets one poisoned creature it can see within 30 feet of it. The target must succeed on a DC 19 Constitution saving throw or fall unconscious until the poisoned condition ends on it.

Sap Life (Costs 2 Actions). The Arachno-Lich targets one creature it can see within 30 feet of it. The target must succeed on a DC 19 Constitution saving throw or take 11 (2d10) necrotic damage. The Arachno-Lich regains a number of hit points equal to the amount of damage that the creature takes.