Briosead, Lord of Black Thorns

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

Special Equipment. Briosead carries a magic shillelagh called Darktether. In the hands of anyone other than Briosead, Darktether is a staff of the magi.

Heart of the Black Thorns (Mythic Trait; Recharges after Short or Long Rest). If Briosead is reduced to 0 hit points he does not die, instead, he regains 200 hit points and gains access to his mythic actions. After he is destroyed a second time, his body transforms into a thornbush with a beating heart inside. The heart is known as the Thornseed and if it is not destroyed in the next 5 days, Briosead will reform his body and seek out his slayers. The Thornseed is an object with an AC of 20 and 30 hit points; it is immune to all damage except radiant damage.

Unusual Nature. Briosead doesn’t require air, food, drink, or sleep.

Turn Resistance. Briosead has advantage on all saving throws against being turned.

Multiattack. Briosead uses Thorn Torrent (if available), Evilseed, or Spellcasting. He then makes two attacks with Darktether.

Darktether. Melee Weapon Attack: +13 to hit, reach 5 ft., one target. Hit: 13 (1d8 + 5) bludgeoning damage plus 12 (2d6) necrotic damage. If the target is a creature, it is afflicted by Dark Druidcraft, taking 12 (2d6) necrotic damage at the start of each of its turns. Immediately after taking this damage on its turn, the target can make a DC 23 Constitution saving throw, ending the effect on itself on a success. Until it succeeds on this save, the afflicted target can't regain hit points.

Torrent of Thorns (Recharge 4–6). Briosead creates a twisting, writhing mass of thorns that follow his mental commands. The mass is as large as and uses the statistics of a purple worm (but it has vulnerability to fire and slashing damage] and goes after Briosead in initative. 

Evilseed. Briosead forms a seed in his hand and targets one creature he can see within 120 feet of himself. The target must make a DC 22 Dexterity saving throw, taking 96 (8d8 + 60) piercing damage on a failed save, or half as much damage on a successful one. A Humanoid killed by this magic twists and contorts as roots and branches sprout from their appendages and they transform into a treant at the start of Briosead’s next turn and acts immediately after Briosead (unless he has used Torrent of Thorns, then they go after the thorn beast) in the initiative order. The treant is under Briosead's control.

Spellcasting. Briosead casts one of the following spells, requiring no material components and using Wisdom as the spellcasting ability (spell save DC 26):

At will: detect magic, dispel magic, levitate, lightning bolt, heat metal, druidcraft, web, knock

3/day each: antilife shell, elemental bane, conjure fey, disintegrate, wall of thorns

2/day each: dimension door, greater invisibility, arcane hand (as an action), storm sphere, steel wind strike, 

1/day each: animal shapes, globe of invulnerability, plane shift (self only), power word pain

Potion Distortion. Briosead causes all potions withing a 120 ft radius to become potion of healing (greater)s. When a creature drinks a transformed potion, they do not gain any benefit from it; instead Briosead gains the benefits of the potion. When a potion is within 10 ft of Briosead, it becomes a potion of healing (supreme).

Spellcasting. Briosead casts a spell with a casting time of one action or less. 

Darktether. Briosead makes an attack with Darktether

Briosead can take two reactions per round but only one per turn.

Corrupted Counterspell. Briosead waves his hands and targets a creature that he can see casting a spell. The caster must succeed an Intelligence saving throw (DC= 13 + level of spell) or the spell will backfire. If it is a damaging spell, it targets the caster; if it is a buff spell, it targets Briosead. On a success the spell functions as normal and that spell cannot be corrupted again.

Thorned Shield. In response to being hit by an attack, Briosead conjures a shield of thorns around him, any creature hitting him with an attack takes 10 (3d6) piercing damage. The shield adds +5 to his AC until the end of his next turn.

 If Briosead's Heart of Black Thorns trait is active, he can use the options below as a legendary actions. Briosead can take 3 mythic actions, choosing from the options below. Only one mythic action option can be used at a time and only at the end of another creature's turn. Briosead regains spent legendary actions at the start of his turn.

Misdirection. Briosead uses magic to make himself appear to be at another location within 40 ft of him. The real Briosead is invisible and stays so until he makes an attack. The illusion moves and sounds as if Briosead were in that spot.

Spellcasting (Costs 2 Actions).  Briosead casts one spell from his Spellcasting feature.

Mythic Might (Costs 3 Actions). Briosead uses Torrent of Thorns or his Evilseed feature