Beveron

Fey Ancestry. Averon has advantage on saving throws against being charmed, and magic cannot put him to sleep.

Archery Fighting Syle.  Averon gains a +2 bonus to attack rolls made with ranged weapons.

Supernatural Defense. Whenever the target of Averon's slayer's prey forces him to make a saving throw and whenever he makes an ability check to escape a grapple, add 1d6 to his roll.

Land's Stride. Moving through nonmagical difficult terrain costs you no extra movement and you can also pass through nonmagical plants without being slowed by them and without taking damage from them. You have advantage on saving throws against plants that are magically created or manipulated to impede movement.

Spellcasting. Averon is a spellcaster. He is spellcasting ability is Wisdom (spell save DC 15, +7 to hit with spell attacks, +3 spell ability mod). Averon has the following Ranger spells prepared:

At will: Hunter's Mark, Zephyr Strike. 
3/day each:  Zone of Truth, Beleth's Black Tentacles, Conjure Volley   
1/day each: Contagion

Extra Attack: Averon takes two attacks per action.

Shortsword attack. Melee weapon attack: +11 to hit, reach 5ft., 1 target.  Hit: 1d6 + 7 piercing damage. Attack.   

Oathbow Attack. Ranged Weapon Attack: +13 to hit, range 150/600 ft., 1 target. Hit: # (1d8 + 7) piercing damage. If the target is your sworn enemy, the attack has advantage, the target cannot benefit from cover other than full cover, and the target takes an additional 3d6 poison damage.

Hunter's Sense. As an action, choose one creature you can see within 60 ft. You immediately learn whether the creature has any damage immunities, resistances, or vulnerabilities and what they are if the creature is not hidden from divination magic. You can use this feature 1 times per long rest.

Actions in Combat.  Two-Weapon Fighting

Spells.  Hunter's mark, Zephyr Strike

Slayers Prey.  As a bonus action, you designate one creature you can see within 60 ft. and the first time each turn that you hit that target with a weapon attack, it takes an extra 1d6 poison damage. This benefit lasts until you finish a short or long rest or if you designate a different creature.

Actions in Combat.  Opportunity Attack

Negate Spell (recharge 5 rounds).  Beveron tries to interrupt a spell he sees a creature casting within 60 feet of him.  If the spell is 3rd level or lower, the spell fails and has no effect.  If the spell is 4th level or higher, Beveron makes a Wisdom check against a DC of 10 + the spell's level.  On a success, the spell fails and has no effect.

Beveron can take 2 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. Beveron regains spent legendary actions at the start of its turn.

Abyssal Magic (costs 1 Action).  Beveron can cast any of the spells he has access to using a legendary action.  Additional, Beveron can instead choose to magically teleport, along with any equipment he is wearing or carrying, up to 120 feet to an unoccupied space he can see.

Absorb (costs 2 actions).  Beveron can choose one of his minions that is within 15ft of him.  Beveron devours the life essence of the target, regaining 3x the minion's CR as HP.

Boss Actions

Beveron can take 3 Boss actions per day.  Only one boss action or legendary can be used at a time and only at the end of another creature's turn.  Beveron regains spent Boss actions at dawn each day.

Taunt.  The Boss taunts their for, or preys on one of their emotional connections.  This can be an act of intimidation or an act of deception.  The target has disadvantage on their next attack.

Stomp.  The boss leaps into the air and stomps the ground, causing a shockwave that effects every creature in a 15ft radius.  Every affected creature must make a STR or DEX saving throw (DC 20). On a failure, the creature takes 6d4 bludgeoning damage and falls prone.  On a success, the creature takes half the damage, and does not fall prone.

Beleth's psychic yell. Once Averon falls below 30 HP, Beleth's mind lashes out at a creature that he can see within 90ft.  Creatures that have an intelligence score of 2 or lower are unaffected.  The target must make an intelligence saving throw.  On a failed save, the target takes 14d6 psychic damage and is stunned.  On a successful save, the target takes half as much damage and isn't stunned.  If the target is killed by this damage, its head explodes, assuming it has one.  A stunned target can make an intelligence saving throw at the end of each of its turns.  On a successful save, the effect ends.