Amania of the Wild Hunt

Fey Ancestry. Amania cannot be magically put to sleep.

Awakened Senses. Amania has advantage on Perception checks to find and track humanoids.

Escape the Horde. Opportunity attacks made against Amania are made at disadvantage.

Magic Resistance. The rider has advantage on saving throws against magical effects.

Mounted Fire Resistance. While mounted, the rider has resistance to fire damage.

Mounted combatant. While mounted and not incapacitated the rider gains the following benefits:

• It has advantage on melee attack rolls against unmounted creatures that are smaller than its mount.
• It can force an attack targeted at its mount to target it instead.
• If the mount is subjected to an effect that allows it to make a Dexterity save to take only half damage, it takes no damage if it succeeds and half damage if it fails.

Undead Fortitude. If damage reduces the rider to 0 hit points, it must make a Constitution saving throw with a DC of 5+ the damage taken, unless the damage is radiant or from a critical hit. On a success, the rider drops to 1 hit point instead.

Spellcasting. Amania is a 10th-level spellcaster. Her spellcasting ability is Wisdom (spell save DC 15, +7 to hit with spell attacks). She has the following Ranger spells prepared:
1st level (4 slots): Absorb Elements, Ensnaring Strike, Hail of Thorns, Hunter's Mark
2nd level (3 slots): Silence
3rd level (2 slots): Conjure Barrage

Cast a spell. 

Multiattack. Amania makes two whip or longbow attacks. It can use a Hooves or Life Drain attack instead of a whip attack. 

Horde Breaker. Once on each of her turns when she makes a weapon attack, Amania can make another attack with the same weapon against a different creature that is within 5 feet of the original target and within range of her weapon.

Longbow. Ranged Weapon Attack: +11 to hit, range 150/600ft., one creature. Hit: 14 (2d8+5) piercing damage. 

Whip. Melee Weapon Attack: +8 to hit, reach 10ft., one creature. Hit: 8 (1d8 + 4) slashing damage.

Hooves. (Mounted only) Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 13 (2d8+4) bludgeoning damage plus 7 (2d6) fire damage. 

Ethereal Stride. (Mounted only) The nightmare and up to three willing creatures within 5 feet of it magically enter the Ethereal Plane from the Material Plane, or vice versa.

Ensnaring Strike. Ensnaring Strike

Hail of Thorns. Hail of Thorns

Hunter's Mark. Hunter's Mark

Absorb Elements. Absorb Elements

Snapshot. As a reaction, when a hostile creature moves to within 5 feet of Amania, she can make an attack of opportunity with the bow and immediately move up 10 feet. This movement does not provoke attacks of opportunity.