At 3rd level, a Paladin gains the Sacred Oath feature. The following option, Oath of Warding, is available to a Paladin, in addition to those offered in official books such as the Player's Handbook.

Oath of Warding

Most Paladins dedicate themselves to fighting all threats in equal measure, or choose to focus on those a little closer to home. Those who swear themselves to the Oath of Warding, however, seek out threats from further away. They pledge to protect their own realm from Outsiders who would do harm - Fey creatures, Fiends, Aberrations, Elementals, and even those Celestials who would bring harm.

While not unthinking zealots, an Oath of Warding Paladin is never comfortable in the company of Outsiders, and is always vigilant lest they need to bring their unique skillset to bear.

Tenets of Warding Protect Purity. Where you find befoulment, purge it. If those from other realms wish harm, cleanse them from your plane with the sword and the flame. Remember the Greater Threat. All evil deserves retribution, but an evil from outsiders is more pressing. It must be responded to before all others, as hard as this may be. Practice Caution. A war on all fronts requires some battles to be postponed. Treat those who come in peace with wariness, and those who do not without mercy. Maintain Your Resolve You may have to overcome great challenges to protect your plane from outsiders. Do not waver from your path, no matter what obstacles lay in your way

Oath of Warding Features Paladin Level Feature 3rd Oath Spells, Channel Divinity 7th Aura of Warding 15th Otherworldly Defense 20th Planar Bastion

Oath Spells You gain oath spells at the paladin levels listed in the Oath of Warding Spells table. See the Sacred Oath class feature for how oath spells work. Paladin Level Spells 3rd absorb elements, detect evil and good 5th earthbind, moonbeam 9th dispel magic, protection from energy 13th banishment, elemental bane 17th banishing smite, hallow

Channel Divinity When you take this oath at 3rd level, you gain the following two Channel Divinity options. See the Sacred Oath class feature for how Channel Divinity works. Impose Vulnerability. As an action, choose one creature within 30 feet of you that you can see. That creature must make a Wisdom saving throw. On a failed save, the creature loses any damage resistances it has. At the end of each of its turns, the creature may repeat the saving throw, and regains its damage resistances on a success. Damage immunities the creature has are not affected by this feature. Preternatural Understanding. As a bonus action, you grant yourself +5 to Intelligence (Arcana) or Intelligence (Religion) checks for the next ten minutes.

Aura of Warding Starting at 7th level, when an enemy within 10ft of you makes a saving throw, you may use your reaction to give them disadvantage on that saving throw. At 18th level, the range of this aura increases to 30 feet.

Otherworldly Defense Starting from 15th level, you gain resistance to Psychic, Radiant and Necrotic damage.