Undead Nature. The Undead Horse does not require Air, Food Water or Sleep

Everlasting Steed. If damage reduces the Undead Horse 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 Undead Horse drops to 1 hit point instead.

Multiattack. The Undead Horse makes Two Rotted Hooves Attacks and uses Grave Neighing if it is Charged

Rotted Hooves. Melee Weapon Attack: +6 to hit, reach 5 ft., 1 target. Hit: 15 (2d8 + 6) Bludgeoning damage Plus 3 (1d6) Necrotic Damage

Grave Neighing (Recharge 6) The Undead Horse unleashes a wailing neigh  to evoke terror of the grave. any creature of the Horses choice within 120 feet that can hear is must make a DC 15 Wisdom saving throw or take 25 (4d8+7) Necrotic Damage and become frightened for 1 minute on failure, or half as much and not become frightened on a success. A creature frightened by the Undead Horse that takes this damage additionally takes 14 (2d6+7) Psychic damage.