Archon of Annexation

Divine Awareness. The Archon of Annexation knows if it hears a lie

Magic Resistance. The Archon of Annexation has advantage on saving throws against spells and other magical effects.

Aura of Subjugation. An aura extends outwards from the Archon in a 30 foot radius. All creatures within this aura must make a DC 25 Wisdom saving throw or be under the effects of the Geas spell. A creature that succeeds the saving throw is immune to this aura for 24 hours.

Innate Spellcasting. The Archon of Annexation's innate spellcasting ability is Charisma (Spell Save DC 25, +18 to hit with spell attacks) It can innately cast the following spells, requiring no material components:

At will: Detect Good and Evil,  Mirror Image, Lightning Bolt (4th Level)

4/day: Dominate Monster, Mass Suggestion (7th Level), Plane Shift (Self Only)

3/day: Blade Barrier, Fire Storm

2/day: Blade of Disaster

Legendary Resistance (4/day). If the Archon fails a saving throw, it can choose to succeed instead.

Iron fist Usurper (5/day). The Archon targets a single creature. Until the end of the Archon's next turn, that creature becomes vulnerable to a damage type of the Archon's choice. If the creature is resistant to the chosen damage type, then the attack acts as if the given creature has neither resistance nor vulnerability. This doesn't function if the target is immune to a given damage type. This trait cannot be used more than once against one target. This trait can be used against multiple creatures at the beginning of the Archon's turns. 

Multiattack. The Archon makes two slam attacks

Slam. Melee Weapon Attack: +16 to hit, reach 15 ft., 1 target. Hit: 27 (3d10 + 9) Bludgeoning damage. 

Overawe Prowess (Recharge 6). The Archon causes soldiers of light to erupt from the ground in a 60 foot radius sphere around the Archon. All creatures in this radius take an initial 20 Radiant damage. Each creature must make a DC 25 Strength saving throw or be pushed back 20 feet in the opposite direction of the Archon. They must continue to make this save until they are out side of the radius.

Menacing Glare (3/day). The Archon imposes disadvantage on an attack against it. If the attack misses and the creature is within 30 feet of the Archon, the creature must be forced to reroll its save against the Aura of Subjugation, regardless of if they succeeded already, and must take the new roll. If the creature is not within 30 feet of the Archon, then they still receive disadvantage but they are not required to reroll the save.

Parry (Blade of Disaster only). The Archon adds a +6 to its AC. To do so, the Archon must see the attacker and must be wielding the Blade of Disaster.

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

Slam. The Archon makes one Slam attack

Cast a Spell (Costs 2 Actions). The Archon casts a spell.

Acheron Volley (Costs 3 Actions). The Archon launches a volley of devastating arrows summoned directly from the plane of Acheron. All creatures within a point the Archon can see within 120 feet in a 40 foot radius must make a DC 20 Dexterity saving throw or take 28 (5d10) Piercing and 28 (5d10) Fire damage. In addition, any creature who fails the save has their movement speed reduced to 0 until the end of their turn.