Count Lazarus Firebrand

Legendary Resistance (3/day): If the creature fails a saving throw, it can choose to succeed instead.

Old one's Tongue: this creature counts as under the spell glibness for all charisma (deception) checks

Ageless: the creature does not suffer the affects of time and spells that would increase his age have no affect

Magical Attacks: weapon attacks from this creature count as magical for the purposes of overcoming resistances

War caster:

the creature has advantage on Constitution saving throws that it makes to maintain its concentration on a spell when it take damage.

it can perform the somatic components of spells even when it has weapons or a shield in one or both hands.

Observant: 

• If the creature can see a creature's mouth while it is speaking a language (creature name) understand, (creature name) can interpret their words by reading their lips.

•the creature have a +5 bonus to your passive Wisdom (Perception) and Intelligence (Investigation) scores.

Firebrand Half Plate: 

This is a set of armor made by Count Lazarus Firebrand using his very essence in the forging process, resulting in a set of armor with the strength of adamantine but the weight of mithril

This suit of armor was made with the soul of an immensely powerful magic being, when wearing it, any critical hit against you becomes a normal hit. additionally, it does not impose disadvantage on stealth checks.

wearing this suit of armor gives the wearer a +3 bonus to their armor class

Half plate consists of shaped metal plates that cover most of the wearer's body. It does not include leg protection beyond simple greaves that are attached with leather straps.

Spellcasting: the creature is a 10th-level spellcaster. Its spellcasting ability is charisma spell save DC 25 to hit with spell attacks). The creature has following wizard spells prepared:
Cantrips (at will): chill touch (4d8), firebolt (4d10), mage hand, shocking grasp (4d8), minor illusion 
1st level (4 slots): Burning hands(dex save,3d6), Charm Person(wis save), disguise self, detect magic, feather fall
2nd level (3 slots): Blindness/deafness (con save), Hold person (Wis save), Misty step
3rd level (3 slots): counterspell, Fireball(Dex save,8d6),Burning hands (Dex save,5d6), Fear (wis save)
4th level (3 slots): polymorph (Wis save), Wall of fire (Dex save, 5d8)
5th level (3 slots):  cloudkill (Con save, 5d8), dominate person (wis save), scrying (wis)
6th level (1 slot): Flesh to stone (con save), Mass suggestion (wis save)
7th level (1 slot): Finger of death (con save, 7d8+30) Reverse gravity (dex save)
8th level (1 slot): Abi-Dalzim’s Horrid Wilting (con save, 12d8), Antimagic field
9th level (1 slot): Psychic scream (Int save, 14d6)

Multiattack: the creature can make up to 4 melee weapon attacks per one action

Mindrender: melee weapon attack +14 to hit, reach 10 ft, hit: (4d8+7) slashing + 3d6 psychic damage

Magical Barrier (5/day): If the creature is targeted by an attack and is hit, it can use its reaction to increase it's AC by it's charisma modifier until the end of its next turn. If a creature's attack is blocked by the magical barrier, the creature gains an attack of opportunity against their attacker

Feather Fall: Choose up to five falling creatures within range. A falling creature's rate of descent slows to 60 feet per round until the spell ends. If the creature lands before the spell ends, it takes no falling damage and can land on its feet, and the spell ends for that creature.

War caster reaction: When a hostile creature's movement provokes an opportunity attack from it, it can use it  reaction to cast a spell at the creature, rather than making an opportunity attack. The spell must have a casting time of 1 action and must target only that creature.

Move: creature moves up to half its speed.

Attack: creature makes one melee weapon attack

Replenish: (creature name) rolls a d20, on a roll of 20, it regains all uses of its magical barrier (uses all 3 legendary reactions)

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Mythic Action Name (Costs # Actions). Enter the description for your mythic action.