Death Knight

When a paladin that falls from grace dies without seeking atonement, dark powers can transform the once-mortal knight into a hateful undead creature with burning malevolent eyes. You become a death knight. You gain the following benefits:

• Undead Nature - You are undead, you do not require air, food, drink, or sleep.
• You are immune to Necrotic and Poison damage.
• You are immune to the Exhaustion, Frightened, and Poisoned conditions. 
• You gain Darkvision up to 120 feet.
• You gain proficiency in Dexterity saving throws.
• Magic Resistance - You have advantage on saving throws against spells and other magical effects.
• Marshal of the Undead - Unless you are incapacitated, you and undead creatures of your choice within 60 feet have advantage on saving throws against features that turn undead.
• Hellfire Orb - Once per day, as an action you can hurl a magical ball of fire that explodes at a point you can see within 120 feet. Each creature in a 20-foot-radius sphere centered on that point must make a Dexterity saving throw against your spell save DC. The sphere spreads around corners. A creature takes 10d6 fire damage and 10d6 necrotic damage on a failed save, or half as much damage on a successful one.
• Parry - As a reaction you can add 6 to your AC against one melee attack that would hit you. To do so, you must see the attacker and be wielding a melee weapon.

Eldritch Power. Your ability to heal is lost, all Radiant damage you inflict is changed to Necrotic instead, and you inflict an additional 4d8 Necrotic damage to all weapon attacks. As a death knight you also attract lesser undead, they are drawn by your presence and respect and carry out your commands to the best of their ability. 

Immortal Until Redeemed.  As a death knight you can arise anew even after you've been killed. Only when you atone for a life of wickedness or find redemption and become of non-evil alignment, the can you finally escape this undead purgatory and truly perish. When you are killed your body and all your equipment fall to ash, you revive in 1d10 days with all of your equipment in the spot where your sins were committed.