Chicomecōātl, The First Anathema

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

Transfigured Body. Unless willing, Chicomecōātl is immune to any spell or magical effect that would alter his physical form.

Legendary Resistance (4/day). If Chicomecōātl fails a saving throw, he can choose to succeed instead.

Ophidiophobia Aura. Any creature of Chicomecōātl's choice, other than a snake or a yuan-ti, that starts its turn within 30 feet of Chicomecōātl must succeed on a DC 18 Wisdom saving throw or become frightened of snakes and yuan-ti. A frightened target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a target’s saving throw is successful or the effect ends for it, the target is immune to Chicomecōātl's aura for the next 24 hours.

Seven Heads. Chicomecōātl has advantage on saves against being blinded, charmed, deafened, frightened, stunned, or knocked unconscious.

War Caster. Chicomecōātl has advantage on Constitution saving throws to maintain concentration on his spells when taking damage.

Mage Slayer. When Chicomecōātl damages a creature concentrating on a spell, that creature has disadvantage on the saving throw it makes to maintain concentration.

Spell Sniper. When Chicomecōātl casts a spell that requires him to make an attack roll, the spell's range is doubled. Additionally his ranged spell attacks ignore half and three-quarters cover.

Arcane Melee. Chicomecōāt’s Claw and Flurry of Bites attacks count as magical for the purpose of overcoming resistances.

Multiattack (Anathema Form Only). Chicomecōātl makes two Claw attacks or uses Spellcasting, and makes one Flurry of Bites attack.

Claw (Anathema Form Only). Melee Weapon Attack: +10 to hit, reach 10 ft., one target. Hit: 20 (4d6 + 6) slashing damage.

Flurry of Bites (Anathema Form Only). Melee Weapon Attack: +10 to hit, reach 10 ft., one creature. Hit: 30 (7d6 + 6) piercing damage plus 17 (5d6) poison damage.

Constrict (Snake Form Only). Melee Weapon Attack: +10 to hit, reach 15 ft., one Large or smaller creature. Hit: 23 (5d6 + 6) bludgeoning damage plus 10 (3d6) acid damage, and the target is grappled (escape DC 16). Until this grapple ends, the target is restrained, and it takes 23 (5d6 + 6) bludgeoning damage plus 10 (3d6) acid damage at the start of each of its turns. The anathema can constrict only one creature at a time.

Spellcasting (Anathema Form Only). Chicomecōātl casts one of the following spells, requiring no material components and using Intelligence as the spellcasting ability (spell save DC 21):

At will: animal friendship (snakes only),acid splash, fire bolt, green-flame blade, infestation, message, ray of frost, magic missile (1st level), shatter (2nd level)

As ritual: comprehend languages, detect magic, identify, magic mouth

1/day each: glyph of warding, fireball, divine word

3/day each: darkness, entangle, fear, polymorph, suggestion

Chicomecōātl is a 20th level wizard with the following spells prepared, using intelligence as his spellcasting ability (spell save DC 21)

1st level (4 slots): comprehend languages, detect magic, earth tremor, expeditious retreat, identify, mage armor, magic missile, shield, sleep

2nd level (3 slots): magic mouth, scorching ray, shatter

3rd level (3 slots): catnap, dispel magic, fireball, glyph of warding, counterspell

4th level (3 slots): polymorph

5th level (3 slots): dominate person, modify memory

6th level (2 slots): chain lightning, circle of death, disintegrate, mass suggestion, sunbeam

7th level (2 slots): crown of stars, draconic transformation, finger of death

8th level (1slot): clone, feeblemind

9th level (2 slot): prismatic wall, true polymorph

Change Shape. Chicomecōātl transforms into a Huge constrictor snake or back into his true form. His statistics are the same in each form. Any equipment he is wearing or carrying isn’t transformed.

War Caster Chicomecōātl uses his Spellcasting action as an opportunity attack, provided the spell has a casting time of one action and targets that creature.

Mage Slayer When a creature within 5ft of Chicomecōātl casts a spell, he makes a melee attack against that creature.

Chicomecōātl can take 5 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature’s turn. Chicomecōātl regains spent legendary actions at the start of his turn.

Claw (anathema form only) Chicomecōātl makes two claw attacks.

Flurry of Bites Chicomecōātl makes one flurry of bites attack.

Spellcasting (Costs 2 actions) Chicomecōātl casts a spell of sixth level or lower.

Form guardians (Costs 3 actions) Chicomecōātl creates two Yuan-ti abomination from the floor, with their creature type being Construct instead of Monstrosity. These Yuan-ti are friendly to Chicomecōātl and are immune to being charmed and poisoned.

Advanced Arcane Recovery (Costs 5 actions) Chicomecōātl recovers spell slots with a combined level of 12 or lower, unlike with standard Arcane Recovery these spell slots can be of any level.