The Oath of the Crown is sworn to the ideals of civilization, be it the spirit of a nation, fealty to a sovereign, or service to a deity of law and rulership. The paladins who swear this oath dedicate themselves to serving society and, in particular, the just laws that hold society together. These paladins are the watchful guardians on the walls, standing against the chaotic tides of barbarism that threaten to tear down all that civilization has built, and are commonly known as guardians, exemplars, or sentinels. Often, paladins who swear this oath are members of an order of knighthood in service to a nation or a sovereign, and undergo their oath as part of their admission to the order's ranks.

Tenets of the Crown

The tenets of the Oath of the Crown are often set by the sovereign to which their oath is sworn, but generally emphasize the following tenets.

Law. The law is paramount. It is the mortar that holds the stones of civilization together, and it must be respected

Loyalty. Your word is your bond. Without loyalty, oaths and laws are meaningless.

Courage. You must be willing to do what needs to be done for the sake of order, even in the face of overwhelming odds. If you don't act, then who will?

Responsibility. You must deal with the consequences of your actions, and you are responsible for fulfilling your duties and obligations.

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.

Champion Challenge. As a bonus action, you issue a challenge that compels other creatures to do battle with you. Each creature of your choice that you can see within 30 feet of you must make a Wisdom saving throw. On a failed save, a creature can't willingly move more than 30 feet away from you. This effect ends on the creature if you are incapacitated or die or if the creature is more than 30 feet away from you.

Turn the Tide. As a bonus action, you can bolster injured creatures with your Channel Divinity. Each creature of your choice that can hear you within 30 feet of you regains hit points equal to 1d6 + your Charisma modifier (minimum of 1) if it has no more than half of its hit points. 

Divine Allegiance

Starting at 7th level, you and friendly creatures within 10 feet of you cannot have their hit point maximum reduced by any means.

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

Notes on changes: I wanted to change this so that the ability would not overlap completely with the newer Oath of Redemption. Instead of taking damage for them, it prevents your HP max from being reduced. 

Unyielding Saint

Starting at 15th level, you have advantage on saving throws to avoid becoming paralyzed or stunned.

Exalted Champion

At 20th level, your presence on the field of battle is an inspiration to those dedicated to your cause. You can use your action to gain the following benefits for 1 hour:

• You have resistance to bludgeoning, piercing, and slashing damage.
• Your allies have advantage on death saving throws while within 30 feet of you.
• You have advantage on Wisdom saving throws, as do your allies within 30 feet of you.
• If you use your Turn the Tide channel divinity option, you can also target creatures within 30 feet that are unconscious to regain hit points. 

This effect ends early if you are incapacitated or die. Once you use this feature, you can't use it again until you finish a long rest.

Notes on changes: Removed the restriction of the BPS resistance to only attacks from nonmagical weapons. Added the benefit that Turn the Tide could be empowered to restore hitpoints to downed allies, not just those that can hear you.  

Death holds no sway over your patron, who has unlocked the secrets of everlasting life, although such a prize – like all power – comes at a price. Once mortal, the Undying has seen mortal lifetimes pass like the seasons, like the flicker of endless days and nights. It has the secrets of the ages to share, secrets of life and death. Beings of this sort include Vecna, Lord of the Hand and the Eye; the dread Iuz; the lich-queen Vol; the Undying Court of Aerenal; Vlaakith, lich-queen of the githyanki; and the deathless wizard Fistandantalus.

In the Realms, Undying patrons include Larloch the Shadow King, legendary master of Warlock's Crypt, and Gilgeam, the God-King of Unther.

Expanded Spell List

Your blood pact allows you to learn from an expanded list of spells when you learn a warlock spell. The following spells are added to the warlock spell list for you

Undying Expanded Spells

Among the Dead

Starting at 1st level, you learn the Spare the Dying cantrip, which counts as a warlock cantrip for you but does not count against the number of cantrips you know. You also have advantage on saving throws against any disease.

Additionally, undead have difficulty harming you. If an undead targets you directly with an attack or a harmful spell, that creature must make a Wisdom saving throw against your spell save DC (an undead needn't make the save when it includes you in an area effect, such as the explosion of Fireball). On a failed save, the creature must choose a new target or forfeit targeting someone instead of you, potentially wasting the attack or spell. An undead is immune to this effect for 24 hours if you target it with an attack or a harmful spell.

Notes on changes: Clarified that the cantrip gained does not count against your number known. For the secondary effect, removed the tidbit that an undead becomes immune to the effect for 24 hours if it succeeds on its saving throw. In other words, you are always protected against undead so long as you do not attack them. 

Indestructible Life

Also at 1st level, you partake of some of the true secrets of the Undying. On your turn, you can use a bonus action to regain hit points equal to 1d8 + your warlock level. Once you use this feature, you can't use it again until you finish a short or long rest.

Starting at 14th level, if you put a severed body part of yours back in place when you use this feature, the part reattaches.

Notes on changes:  This ability is very similar to a fighter’s second wind (but weaker) so I think there is no issue with it being introduced at 1st level instead of 14th. The ability to attach body parts is still withheld until later. 

Defy Death

Starting at 6th level, you can give yourself vitality when you cheat death or when you help someone else cheat it. You can regain hit points equal to 1d8 + your Constitution modifier (minimum of 1 hit point) when you succeed on a death saving throw. Alternatively, when you stabilize a creature with Spare the Dying, you or the targeted creature can regain hit points equal to 1d8 + your Constitution modifier (minimum of 1 hit point).

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

Notes on changes: Since this is a once/long rest feature, I see no harm in allowing you to heal another creature when you defy death instead of just yourself. 

Undying Nature

Beginning at 10th level, you age at a slower rate. For every 10 years that pass, your body ages only 1 year, and you are immune to being magically aged. You also gain the following benefits: 

• While making death saving throws, you score a critical success on a roll of 19 or 20 on the d20. 
• You can remove one level of exhaustion as part of a short rest.

Notes on changes: I wanted to make this feature less similar to the newer Undead patron feature. To reflect its resistance to death, I figured giving it a higher chance of success on death saves and the ability to remove exhaustion more easily would mechanically reflect that and make the ability stronger. 

Mastery Over Death

When you reach 14th level, you have obtained the power to evade death granting the following benefits:

• The hit points restored by your Indestructible Life and Defy Death feature are now determined by rolling 2d8 instead of 1d8. 
• You succeed on death saving throws on a value of 8 or higher on the d20
• You can cast Spare the Dying as a bonus action 

Notes on changes: Completely new ability that builds off of this warlock's other features to make them more impactful at higher level.