Bravest. The adamantine guard cannot be frightened and all allies who can see the adamantine guard have advantage on saves against frightened

Warrior. The adamantine guard deals 3 extra damage die on weapon attacks (included in the attack)

 Adamantine Armor. Any critical hit on the adamantine guard becomes a regular hit.

Multiattack. The Adamantine guard makes four melee attacks. and uses frightful presence

+6 Longsword. Melee Weapon Attack: +21 to hit, reach 5 ft., one target. Hit: 32 (4d8 + 15) slashing damage. plus 14 (4d6) fire damage.

Leadership (6/Day). For 1 minute, the adamantine guard can utter a special command or warning whenever a nonhostile creature that it can see within 30 feet of it makes an attack roll or a saving throw. The creature can add  2d10 to its roll provided it can hear and understand the knight. A creature can benefit from only one Leadership die at a time. This effect ends if the knight is incapacitated.

Frightful Presence. Each creature of the Adamantine guards choice that is within 120 feet of the Adamantine guard and aware of it must succeed on a DC 18 Wisdom saving throw or become frightened for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the Adamantine guards Frightful Presence for the next 24 hours.

Parry. The Adamantine guard adds 6 to its AC against one melee attack that would hit it. To do so, the knight must see the attacker and be wielding a melee weapon.

The Adamantine Guard 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. The Adamantine Guard regains spent legendary actions at the start of its turn.

Commanding Shout. The Adamantine Guard makes an intimidation check at advantage against everyone within 30 ft

Sweep Attack. The Adamantine Guard makes a Longsword attack at every creature within melee.

Fiery Release (Costs 3 Actions). The Adamantine Guard Slams their sword into the ground and releases a fiery explosion. Each creature within 20 feet of the Adamantine guard must succeed on a DC 18 Dexterity saving throw or take 54 (8d10 + 10) Fire damage damage and be knocked prone. half damage on success and the creature is not knocked prone