Oath of the Infernal

Paladins who swear this oath are sworn into a life of ambition.  Most of those who make this deal have something planned beforehand be it vengeance, power, money, or anything that people are ambitious for.  Breaking the oath is a difficult process due to its nature being more like a contract and less of a vow.  Becoming an oathbreaker would be incredibly difficult but still possible.

Channel Divinity

When you take this oath at 3rd level, you gain the following two Channel Divinity options.

Infernal Protection. As a bonus action, you can grant a living creature some of the resilience of the Nine Hells using your Channel Divinity.  One creature of your choice is granted magic resistance for 1 minute.

Frightening Gaze. As an action, you can look at a group of creatures and by using your Channel Divinity, instill intense fear into them.  When you use this Channel Divinity option, you can force an amount of creatures up to your charisma modifier to make a wisdom saving throw.  On a failed save, the creature is frightened for 1 minute.  On a successful save, the creature is not frightened.

Oath Spells

You gain oath spells at the paladin levels listed.

Oath of the Infernal Spells

Aura of Perception

Starting at 7th level, you and friendly creatures within 10 feet of you are granted Devil's Sight.

At 18th level, the range of this aura increases to 30 feet.

Devil Enforcer

Beginning at 15th level, you are able to summon a devil from the Nine Hells that is loyal to the one your oath is sworn to for it to do your bidding.  Using your action, you can summon a devil with CR 9 or lower and stays with you for up to an hour or until you dismiss it.  During it's time with you, the devil can't take any hostile actions against you as it is loyal to your devil boss but it doesn't have to obey your commands if it perceives them as foolish or suicidal.  The devil takes its turn directly after yours.  At the end of your turn, you can give the devil a command, using no action on your part, and if the devil sees it as beneficial to itself or its plans, it acts on that command.  If there is a demon or other force of chaos nearby that is hostile towards you or the devil, it prioritizes snuffing out chaotic individuals over something more neutral or orderly.

Once you do this you cannot do it again until after your next long rest.

Infernal Ascension

At 20th level, as an action, you can harness the power of an archdevil to bring down your foes.  For up to 1 hour, you start to turn into a devil.  Large batlike wings sprout from your back, you grow a trident tipped tail if you have no tail already, and you grow a pair of horns if you have none already.

During the duration of the transformation you have a flying speed of 60 feet.  

In addition, for the duration, you have 2 legendary resistances and resistance to nonmagical bludgeoning, piercing, and slashing damage.

Finally, when you attack during the duration, your attacks add 4d10 fire damage to when they hit.

Once you use this feature, you can’t use it again until you finish a long rest.