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

Magic Resistance. The concordant dragon has advantage on saving throws against spells and other magical effects.

Innate Spellcasting. The adult concordant dragon's innate spellcasting ability is Wisdom. The adult concordant dragon can innately cast the following spells, requiring no material components:

At will: Detect good and evil (detects the creatures whole alignment)

3/day each: invisibility, scrying

1/day each: nondetection, true seeing

Multi attack. The adult concordant dragon can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +13 to hit, reach 10 ft., 1 target. Hit: 18 (2d10 + 7) piercing damage. 

Claw. Melee Weapon Attack: +13 to hit, reach 5 ft., 1 target. Hit: 14 (2d6 + 7) slashing damage. 

Tail. Melee Weapon Attack: +13 to hit, reach 10 ft., 1 target. Hit: 16 (2d8 + 7) bludgeoning damage. 

Frightful Presence. Each creature of the dragon’s choice that is within 120 feet of the dragon and aware of it must succeed on a DC 17 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 dragon’s Frightful Presence for the next 24 hours.

Antithetical breath (Recharges 5/6. The concordant dragon exhales a blast of antithetical energy, each creature within a 65ft cone must make a DC 20 Wisdom saving throw or take 32 (13d4) damage if the creature has a neutral part to their alignment or if they aren't neutral 65 (26d4) damage. On a successful saving throw a creature takes half damage. 

Variant: Summon rilmani (1/Day). The concordant dragon chooses what to summon and attempts a magical summoning.

An adult concordant dragon has a 75 percent chance of summoning 1d2 + 1 ferrumach. 

A summoned rilmani appears in an unoccupied space within 60 feet of its summoner, acts as an ally of its summoner, and can’t summon other rilmani. It remains for 1 minute, until it or its summoner dies, or until its summoner dismisses it as an action.

The adult concordant dragon 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 adult concordant dragon regains spent legendary actions at the start of its turn.

Detect (Costs 1 Actions). The dragon makes a Wisdom (Perception) check.

Tail attack (Costs 1 Actions). The dragon makes one tail attack. 

Judge soul (Costs 2 Actions). The concordant dragon chooses up to three creatures they can see within 100ft and those creatures must make a DC 20 Charisma saving throw or have one of the following effects occur depending on their alignment. 
Good: The creature can't make any harmful actions on their next turn. 
Neutral: The creature becomes vulnerable to all damage from the next attack that hits them. 
Evil: The creature becomes frightened until the end of their turn and takes 1d12 radiant damage per creature they are within 30ft radius of when they end their next turn.