You have broken your sacred Oath in pursuit of power and ambition. Only darkness remains to fuel you now.
Oath
Unlike other Paladins, Oathbreakers have broken their original oath. For more details, see Oaths and Oathbreaking.
Subclass Features
This subclass obtains all the features from its base class, Paladin, in addition to its unique features outlined below.
Level 1
Channel Oath Ability: Steep an enemy in the darkness that churns within you. The target takes 1d4 + Charisma Modifier
Necrotic damage each turn and Attack Rolls against it have 
Advantage.
Level 3
- Channel Oath Ability: Use the power of your Oath to gain control over an undead creature. The undead will follow you around and attack your enemies. The target's level must be lower than yours.
- Channel Oath Ability Let your darkest emotions burst forth as a menacing pulse to
nearby enemies.
Oath Spells
- You gain additional spells from the darkness within. They are Always Prepared.
Level 5
Oath Spells
- You gain additional spells from the darkness within. They are Always Prepared.
Level 7
- You and any nearby fiends (and undead) gain additional damage to melee weapon attacks equal to your Charisma Modifier. The aura disappears if you fall Unconscious.
Level 9
Oath Spells
- You gain additional spells from the darkness within. They are Always Prepared.
External Links
Oathbreaker on the Forgotten Realms Wiki