Raven Knight

A Raven Knight is fearsome in battle, fusing martial prowess with strange abilities gifted by the Raven Queen. Many Raven Knights work alone, though some may find a small band of companions to aid them in battle, and some may even command and lead entire armies into battle. Masters of death, Raven Knights seek to protect those who cannot protect themselves from undeath and the afterlife. Powerful Raven Knights may even become champions of the Raven Queen, and thus champions of the battlefield.

Original by reddit user u/king_starman. Credit goes to them for a majority of ideas and class features in this subclass.

Knowledge of Death

When you choose this Archetype at 3rd level, you gain proficiency in the Investigation and Medicine skills. Additionally, you can make Intelligence (Investigation) and Wisdom (Medicine) checks with advantage when attempting to determine the cause of death of a creature.

Soul Severing

Feather Step

At 7th level, you move with the grace of the raven. Your walking speed increases by 10ft. Additionally, as a bonus action you gain a flight speed equal to your walking speed until the end of your turn, if you end your turn in midair you begin to fall.

Queens Blessing

At 10th level, the Raven Queen grants you a blessing. You gain advantage on death saving throws, immunity to the frightened condition, and resistance to necrotic damage.

Deaths Embrace

At 15th level, when you or an ally you can see critically hit a creature, you can use your reaction to add 3d10 necrotic damage to the attacks damage roll. You can use this feature a number of times equal to your proficiency bonus. You regain all expended uses of this feature upon completing a long rest.

Duty in Death

At 18th level, when you are reduced to 0 hitpoints or killed outright you can use your reaction to make a weapon attack against the creature within your attack range. On a hit you critically hit that creature and regain hitpoints equal to the damage dealt. You can do this once per long rest.