Undead Unicorn.

Charge. If the Undead Unicorn moves at least 20 ft and hits with its horn attack on the same turn the target takes an extra 9 (2d8) piercing damage.

  Innate Spellcasting: the unicorns innate spellcasting is Charisma (spell save DC 14) the Undead Unicorn can inertly cast the following spells, requiring no components.

 At will: detect evil and good, pass without trace.

 Magic and Necrotic Residence: the Undead Unicorn gets advantage on any saving throws against spells or magical items/weapons. and advantage on saving throws angst weapons that deal necrotic damage.

Multiattack the unicorn makes two attacks one with its horn and the other with its hooves.

Hooves Melee attack: 7+ to hit, reach 5 ft, one target. Hit 11 (2d6+4) Bludgeoning Damage

 Horn Melee Attack: +7 to Hit. Reach 5 ft, One Target. Hit: 8 (1d8+4) Piercing Damage. 

 Rotted Touch: Ff the Unicorn touches a target with its horn that target must make a DC 14 Dexterity saving throw or take 1d8 Necrotic Damage. 

The Undead Unicorn can take 2 Legendary actions from the options listed below, only one Legendary action can be used at a time and only at the end of another creatures turn. the Undead Unicorn regains pent Legendary actions at the start of its turn.

Hooves. The Undead Unicorn makes an attack with its hooves.

Necrotic Shield (Cost 2 Actions). The Undead Unicorn treats a shimmering shield that would have been beautiful in Life around d a creature within 60 ft that it can see. the targeted creature gets -2 to its AC until the end of the Undead Unicorns turn.

Heal self (Cost 3 Actions). The Undead Unicorn magically regains 11 (2d8 + 2) hit points.