Holy Symbol:

Your Holy Symbol is cracked and it has a dark glow to it, seemingly absorbing light.

 

(Advanced Ruleset):

You can decide with your GM, that all healing spells (e.g. Cure Wounds) now only heal undead and contructs and otherwise deal necrotic damage instead to a creature. You can only heal yourself.

Also your body and soul is corrupted by necromatic energy, which alters your appearance, but also your spells and abilities. Starts at level 1.

Spells:

All Spells which would deal radiant damage, deal frost damage instead.

 

Divine Smite (Corrupted):

Your divine smite deals frost damage instead.

 

Lay on Hands (Corrupted):

Your once holy touch has become corrupted. As an action your "Lay on Hands" deals frost damage to an creature instead of healing it. This has no effect on undead or contructs. You can also target yourself as an action and heal yourself.

 

Channel Divinity

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

Frostbrand. As an action, you can imbue one weapon that you are holding with energy, using your Channel Divinity. For 1 minute, you add your Charisma modifier to attack rolls made with that weapon (with a minimum bonus of +1). The weapon also emits  a blue light in a 20-foot radius and dim light 20 feet beyond that. If the weapon is not already magical, it becomes magical for the duration.

You can end this effect on your turn as part of any other action. If you are no longer holding or carrying this weapon, or if you fall unconscious, this effect ends.

Deathgrip: As an action, you grab a creature (which you can see in a 60f radius) which is smaller or one size taller than you, telekinetically and pull it in a free space before you. The target must succeed a Strength Saving Throw to resist this effect. You can also move the creature upward, but not further than the maximum range of the spell (60feet). A lifted creature is suspended in mid-air for one minute as long as the caster is concentrating. While in the air the creature is considerd grappled and can make a wisdom saving throw as an action to break free from it.

 

Oath Spells

You gain oath spells at the paladin levels listed.

Oath of Devotion Spells

PALADIN LEVEL	SPELLS
3rd	armor of agathys, create or destroy water
5th	dragons breath, hold person
9th	elemental weapon, water walk
13th	freedom of movement, shadow of moil
17th	steel wind strike, destructive wave

Aura of Frost

You and allies within 10 feet gain resistance to cold damage, and don't suffer the effects of extreme cold, as described in the Dungeon Master's Guide. The aura extends 10 feet from you in every direction, but not through total cover.

Also frost and ice constantly cristallizes around your weapon. The deathknight gains a bonus to melee weapon damage rolls equal to the Charisma modifier (minimum of +1)

 

Obliterate

Beginning at 15th level, you can freeze the ground around you and even the blood of your enemys. As an action you cause the ground (in a 20f radius) to freeze and small ice shards emit out of the ice. Every creature besides the paladin instantly suffers 8d8 cold damage and have disadvantage to attack rolls and skill checks, as long as they stay inside the radius. A succesful stamina saving throw halfs the damage and negates the effect. The terrain is also considered diffcult terrain. A creature moving through the terrain takes 1d8 frost damage for every 5 feet. A succesful dexterity saving throw negates this effect. The paladin ignores the difficult terrain and its side effect.

These effects last up to one minute and the paladin needs a long rest to regain this feature or can expend a 5th level spellslot to regain this feature.

 

Pillar of Ice

Starting at 20th level, cause ice and frost to permanently hangs from your your body. You gain resistance to all damage and your melee weapon attacks score a critical hit on a 19 or 20.

Also your Obliberate doesnt affect allied creatures anymore.