Ashen Rider

Two Beings. The rider has advantage on Wisdom (Perception) checks and on saving throws against being blinded, charmed, deafened , frightened, stunned, and knocked unconscious.

Superior Invisibility. as a bonus action, the rider can magically turn invisible until its concentrations ends (as if concentrating on a spell). Any equipment the dragon wears or carries is invisible with it.

Flyby. The rider doe not provoke an opportunity attack when it flies out of an enemies reach.

Multiattack. Two with sickle, one with bite.

Sickle. Melee Weapon Attack: +14 to hit, reach 10 ft., 1 target. Hit: 42 (5d12 + 7) [slashing] damage. The creature then takes an additional 5d12 radiant damage. 

Bite. Melee Weapon Attack: +14 to hit, reach 10 ft., 1 target. Hit: 42 (5d12 + 7) [piercing] damage. 

Celestial Guidance (Recharge after a short or long rest). For 1 minute, the rider can utter a special command or warning whenever a non hostile creature that it can see within 30 feet of it makes an attack roll or a saving throw. the creature can add a d12 to its roll provided it can hear and understand the rider. a creature can benefit from only one die at a time. this effect ends if the archon is incapacitated.

Smite (1/Day). Target creature within 120 ft must make a Dexterity saving throw DC 21. On a fail the target takes 200 radiant damage or half as much on a successful one.

Riders Wrath. When the Ashen Rider is reduced to 0 HP the rider make a reaction to use the Smite action even if it has been used today.