A knight who has established a contract with the infernal powers of hell, known as the Hellsworn.  

Hellfire Weapon

As an action, you can wreathe a weapon that you are holding with the fires of hell, using your channel divinity.  For 1 minute, you add your charisma modifier in fire damage dealt by an attack from that weapon (minimum bonus of +1). the weapon also emits bright light in a 10 ft radius and dim light 10 ft beyond that. If the weapon is not already magical it becomes magical for the duration.

When you first use this channel divinity or as an action later on, you may immediately end this effect by slamming your weapon into the ground, unleashing a line of hellfire 30 ft long and 5 ft wide in the direction you are facing.  Each creature in the line must make a Dexterity saving throw against your spell DC.  A creature takes 4d6 fire damage on a failed save, or half as much on a successful save.

At 9th level this damage increases to 6d6 at 17th level the damage increases to 8d6.

You may end this effect with no action on your turn. If you are no longer holding the weapon, or if you fall unconscious, the effect ends.

Turn Adversary

As an action, you present the holy symbol of your contract holder and speak an indictment of the enemies of Hell, using Channel Divinity.  Each aberration, celestial,elemental, or non-lawful fiend that can see of hear you within 30 ft mush make a Wisdom saving throw.  If the creature fails its saving throw, it is turned for 1 minute or until it takes damage.

A turned creature must spend its turns trying to move as far away from you as it can, and it can't willingly move to a space within 30 feet of you.  It also can't take reactions.  For its action, it can use only the Dash action or try to escape from an effect that prevents it from moving. If there is nowhere to move, the creature can use the dodge action.

Fiendish Smite

At 3rd level, your Divine Smite no longer deals radiant damage, and instead deals your choice of either fire or necrotic damage. Your may choose which damage type to use each time your use your Divine Smite feature.

Hellgate

At 7th level,  your connection to your contract grants you and allies within 10 ft radius fire resistance.  You may also activate the hellgate aura that causes 1d8 fire damage to any enemy within the same radius for 1 minute.  Requires a short rest to activate again.

At 18th level, the distances listed in this ability increase to 30 feet.

Infernal tongue

Accepting a contract with Infernal powers gives the paladin the ability to understand the language of Infernals.

Brimstone Blessing

At 15th level, you can channel the power of  your contract to imbue yourself with an unnatural vitality. As a bonus action on your turn, you can gain an amount of temporary hit points equal to your charisma modifier (MINIMUM 1)

Additionally, no matter what you say, magic that would determine if you are telling the truth indicates you are being truthful, if you so choose, and you can't be compelled to tell the truth by magic.

Infernal Inheritor

At 20th level, your contract near completion, and you can assume the mantle of your contract-holder, fully commanding an aspect of their power.  This immense power partially transforms you, toughens your skin, and causes you to grow a foot or two taller and sprout horns and claws, making you perceptibly reminiscent of your contract holder.

You may transform using your action on your turn. If you do, you gain the following benefits for 1 minute.

Darkvision out to 120 feet, or existing darkvision increases by 120 feet.

As a bonus action on your turn, you may make an attack with your claws, which are considered a finesse weapon with which you have proficiency.  These claws deal 1d6 plus your Strength or Dexterity modifier slashing on a hit. You may make this attack even if both your hands are otherwise occupied.

Whenever you deal damage, you deal an additional 2d6 fire damage

Damage you deal ignores resistance and immunity

You have resistance to bludgeoning , piercing, and slashing damage from nonmagical weapons that are not silver.

Once you use this feature, you cannot use it again until you finish a long rest.