Archmage Gromph Baenre

Armor of Spiders (Mythic Trait; Recharges after a Short or Long Rest). If Gromph is reduced to 0 hit points, he doesn’t die or fall unconscious. Instead, he regains 100 hit points. In addition, demonic spiders immediately swarm over his body to protect him, granting him 100 temporary hit points.

Legendary Resistance (3/Day). If Gromph fails a saving throw, he can choose to succeed instead.

Special Equipment. Gromph wears a Robe of the Archmagi

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

Portent (Recharges after Gromph Casts a Divination Spell of 1st Level or Higher).When Gromph or a creature he can see makes an attack roll, a saving throw, or an ability check, Gromph can roll a d20 and choose to use this roll in place of the attack roll, saving throw, or ability check.

Boon of High Magic. Gromph gained one extra 9th-level spell slot.

Boon of Immortality. Gromph stopped aging. He is immune to any effect that would age him, and he can’t die from old age.

Spellcasting. Gromph is an 20th-level spellcaster. his spellcasting ability is Intelligence (spell save DC 24, +16 to hit with spell attacks). Gromph can cast shield and mirror image at will, can cast counterspell and bestow curse once each without spending a spellslot and has the following wizard spells prepared:

Cantrips (at will): fire bolt, light, mage hand, prestidigitation, shocking grasp

1st level (4 slots): detect magic, identify, disguise self, magic missile

2nd level (3 slots): detect thoughts, scorching ray, misty step

3rd level (3 slots): counterspell, lightning bolt, bestow curse, dispel magic, slow

4th level (3 slots): banishment, dimension door, ice storm, summon greater demon

5th level (3 slots): cone of cold, scrying, wall of force

6th level (2 slots): globe of invulnerability, chain lightning

7th level (2 slots): teleport, delayed blast fireball

8th level (1 slot): maze

9th level (2 slots): blade of disaster, Psychic Scream

Fire Bolt. Ranged Spell Attack: +16 to hit, range 120ft., one target. Hit: 22 (4d10) fire damage.

Shocking Grasp. Melee Spell Attack: +16 to hit, reach 5ft., one target. Hit: 18 (4d8) lightning damage and it can't take reactions until the start of its next turn. Gromph has advantage on the attack roll if the target is wearing armor made of metal. 

Scorching Ray. Ranged Spell Attack: +16 to hit, range 120ft., one target. Hit: 7 (2d6) fire damage.

Magic Missle. Ranged Spell Attack:  range 120ft., one target. Hit: 7 (1d4 + 1) force damage.

Blade of Disaster. Melee Spell Attack: +16 to hit, reach 5ft., one target. Hit: 26 (4d12) force damage. or Hit: 78 (12d12) force damage on a critical hit (18 or higher)

Summon Servant (1/Day). Gromph magically summons a retriever or a yochlol. The summoned creature appears in an unoccupied space within 60 feet of its summoner, acts as an ally of its summoner, and can’t summon other demons. It remains for 10 minutes, until it or its summoner dies, or until its summoner dismisses it as an action.

Shield. Gromph gains 5 AC untill the start of his next turn.

Counterspell. Gromph attempts to interrupt a creature in the process of casting a spell. If the creature is casting a spell of 3rd level or lower, its spell fails and has no effect. If it is casting a spell of 4th level or higher, Gromph must make an ability check using its spellcasting ability. The DC equals 10 + the spell's level. On a success, the creature's spell fails and has no effect.

Gromph can take 3 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. Gromph regains spent legendary actions at the start of his turn.

Cast a Spell (Costs 1–3 Actions). Gromph expends a spell slot to cast a 1st-, 2nd-, or 3rd-level spell that he has prepared. Doing so costs 1 legendary action per level of the spell. A cantrip costs 1 action.

if Gromph's mythic trait is active, he can use the options below as legendary actions, as long as he has temporary hit points from his Armor of Spiders.

Cast a Spell (Costs 3 Actions). Gromph expends a spell slot to cast a 4th-level spell that he has prepared. 

Recharge Summon Servant (Costs 3 Actions). Gromph recharges his Summon Servant abillity (can only be used once a day)