Well DnD is going to fight some Devils, so lets make some characters that can do just that!  I always think paladins first, so here we go.

 

Oath of Hell’s Gates

The Oath of Hell’s Gates is an order dedicated to keeping the fiends of hell where they belong-on the prison that is hell by forming the literal Gate that holds them in.  Champions of this order form a bulwark to save any and all who fall afoul of devils by creating the walls that hold the horrors back.

Many who swear this oath are devoted to good gods regardless of law or chaos law focusing on the good they can do and the lives they can save.  Order is important to these champions but order at the cost of rightness is the way of the devils.  Seeing as they see themselves at the walls holding hell back they incorporate images of flaming gates  into their helmets or coats of arms.

Tenets of Devotion

Unlike other orders, these nights hold only two things sacred-help the helpless and stop the fiend.  All other goals are secondary allowing for a large amount of variability among their ranks as paladins of trickster gods mix with true knights of law and order.  All are bound by the cause of helping and defending, so disagreements among them, while often, are short lived.

Oath Spells

You gain oath spells at the paladin levels listed.

Channel Divinity

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

Divine Shield: As a bonus action, you can imbue one shield with divine power.  This shield now floats freely near you and can move up to  up to 30 feet away.  This shield becomes a +1 magic shield if not already magical.  Each turn as a free action, you can choose one target within range and the shield will move to that target providing its bonus to AC as well as the same bonus to Dexterity saves to that target.  At level 7, your shield becomes a +2 magic shield, and at level 15 your shield becomes a +3 magic shield.

You can end this effect on your turn as part of any other action. If you fall unconscious, this effect ends.  While this is in effect, you are still considered to be wielding the shield for all abilities and effects requiring you to be wielding a shield.

Exorcise. As an action, you present your holy symbol and speak a prayer censuring fiends, using your Channel Divinity. Each fiend that can see or hear you within 30 feet of you must make a Wisdom saving throw. If the creature fails its saving throw, it is turned for 1 minute or until it takes damage.  This includes are targets that are currently possessing another creature in range.  Manifesting this power in this way causes the possessing creature to leave, but the possessed creature is freed from the possession.

An exorcised 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’s nowhere to move, the creature can use the Dodge action.

Aura of Protection

Starting at 7th level, you and friendly creatures within 10 feet of you gain the AC and Dexterity saving throws granted by your Divine Shield channel divinity power.

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

Shield the Weak

Beginning at 15th level, as a free action you can voluntarily take all damage a target under your Aura of Protection or Divine Shield would take.  You may not reduce this damage in any way if you choose to take this damage.

Wall for the Gods

At 20th level, as a bonus action, you manifest the true will of heaven to protect your people.  You become a sunburst of divine energy for as long as you can muster it.  All allies and yourself under the effect of your Aura of Protection become immune to damage, have advantage on all attacks, saves, and checks while enemies in the aura have disadvantage on all attacks, saves, and checks.  At the start of each turn, you take 30 radiant damage that can not be reduced, redirected, or prevented due to you manifesting pure divine energy in your mortal frame.  You can end this effect on your turn as part of any other action. If you fall unconscious, this effect ends.