Brandr Helmm, Iron Emperor

Imprenetrable Armor. While wearing his armor, Brandr Helmm ignores damage if the amount of damage dealt is less than 20 (before resistances aply), if its more than 20, it hits as normal. 

Extra training. Brandr Helmm can get a critical hit when he rolls a 18, 19, or 20 on an attack roll.

Holy Acuracy (3/day). When Brandr Helmm misses with a weapon attack, he may choose to make it hit instead.

Weak Points (Mythic Trait; Recharges after a Short or Long Rest). When Brandr Helmm is reduced to 0 hit points, it doesn't die or fall unconscious. Instead, the damage creates cracks in its armor, revealing its weak points. Brandr Helmm has
four weak points: two on each of its shoulders, one on its back, and one at the abdomen. A weak point has an AC of 22 and 100 hit points. It is immune to bludgeoning, piercing, and slashing damage from non magical attacks, and it is inmune to all conditions. If it is forced to make a saving throw, treat its ability scores as 10 (+0). If it finishes a short or long rest, the armor repairs, any destroyed weak points regenerate, and the weak points are covered again. Brandr Helmm dies when all the weak points are destroyed.

Immutable Form. Brandr Helmm is immune to any spell or effect that would alter its form.

Innate Spellcasting. Brandr Helmm's innate spellcasting ability is Wisdom. It can innately cast the following spells, requiring no material components:

 At will: mending, guiding bolt, shield of faith, spiritual weapon

3/day each: spirit guardians, guardian of faith, holy weapon, flame strike    

1/day each: blade barrier, harm, earthquake, gate, wish 

Indomitable. Brandr Helmm can reroll a saving throw it fails. It must use the new roll.

Runes of Protection. At the beginning of each of it's turn, Brandr Helmm can choose three types of damage and become inmune to them until it chooses another types of damage. The options to choose from are: acid, cold, fire, lightning, thunder, radiant, necrotic, force.

Siege Monster. Brandr Helmm deals double damage to objects and structures.

Survivor. Brandr Helmm regains 20 hit points at the start of its turn if it has at least 1 hit point but fewer hit points than half its hit point maximum.

Multiattack. Brandr Helmm makes five weapon attacks or he casts Guiding Bolt thrice.

Summoned Melee Weapon. Melee Weapon Attack: +17 to hit, reach 10 ft., one target. Hit: 28 (3d12 + 9) bludgeoning, piercing or slashing damage (Brandr's choice).

Shield Charge. Brandr Helmm moves up to 30 feet in a straight line and can move through the space of any creature smaller than Large. The first time it enters a creature's space during this move, it makes a shield attack against that creature. If the attack hits, the target must also succeed on a DC 21 Strength saving throw or be pushed ahead of Brandr Helmm for the rest of this move. If a creature fails the save by 5 or more, it is also knocked prone and takes 18 (3d6 + 8) bludgeoning damage, or 29 (6d6 + 8) bludgeoning damage if it was already prone.

Unbreakable Shield of Conquest. Melee Weapon Attack: +17 to hit, reach 10 ft., one creature. Hit: 19 (3d6 + 9) force damage. If the target is a Medium or smaller creature, it must succeed on a DC 21 Strength saving throw or be knocked prone.

Bashing Defence. Brandr Helmm adds 6 to his AC against one melee attack that would hit him. Whether the attack hits or misses, Brandr Helmm can make a Shield attack against the attacker.

Unyielding. When Brandr Helmm is subjected to an effect that would move him, knock him prone, or both, he can use his reaction to be neither moved nor knocked prone.

Brandr Helmm 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. Brandr Helmm regains spent legendary actions at the start of its turn.

Weapon Attack. Brandr Helmm makes a weapon attack.

Light Bolt. Brandr Helmm casts guiding bolt at a creature within range.

Attracting Force (Costs 2 Actions). A 30-foot-radius sphere of crushing force forms at a point you can see within range and tugs at the creatures there. Each creature within 30 ft of Brandr Helmm must make a DC 21 Constitution saving throw. On a failed save, the creature takes 5d10 force damage, and is pulled in a straight line toward Brandr Helmm, ending in an unoccupied space as close to him as possible. On a successful save, the creature takes half as much damage and isn't pulled.

lf Brandr Helmm's mythic trait is active, it can use the options below as legendary actions for 1 hour after using Weak Points.

Weapon Attack. Brandr Helmm makes three weapon attacks or casts guiding bolt twice.

Action Surge (Costs 3 Actions). Brandr Helmm can have another turn, having an additional action, bonus action and movement at its disposal.