Ghost knight

The Order of Knights Incorporeal, or Ghost Knights,
 arose in the principalities of Morgau and Doresh. Fighters
 who follow the Ghost Knight archetype draw power from
 undeath and bring themselves closer to that grim fate in
 service to their vampiric and ghoulish masters.

BONUS PROFICIENCY

Beginning when you choose this archetype at 3rd level, you
 gain proficiency in the Animal Handling skill.

PALE RIDER

Also at 3rd level, you can cast find steed.steed. The steed created
 is an undead creature that takes the form of a ghostly pale
 or dappled riding horse. Your GM can substitute a camel,
 a mastiff, or another mount appropriate to your character.
 When you reach 7th level, a ghostly, undead warhorse
 becomes available.
You can cast this spell once, and regain the ability to do so
 when you finish a long rest. While riding your mount, you
 can use a bonus action to have the steed make one attack.

FRIGHTFUL CHARGE

Starting at 7th level, when you move at least 20 feet and attack a creature, it must succeed on a Wisdom saving throw (DC = 8 + your proficiency bonus + your Charisma modifier) or become frightened of you until the start of your next turn.

TAINT OF UNDEATH

At 10th level, the foul nature of the undead begins overtaking you. You no longer need to eat or drink, and you are immune to being frightened. You take on a pale or waxy appearance that the living find disturbing. You have advantage on Charisma (Intimidation) checks made against living creatures.

GRAVESTRIKE

Starting at 15th level, your weapon attacks deal an additional 1d8 necrotic damage, and you have resistance to necrotic damage.

GHOST RIDER

At 18th level, as a bonus action, you and your mount become ghostly and insubstantial for 1 minute. You gain resistance to bludgeoning, slashing, and piercing damage from nonmagical attacks, and you can move through creatures and objects as if they were difficult terrain, but you take 5 (1d10) force damage and are pushed to the nearest open space if you end your turn inside an object.