Pact of the Lich King

Through whatever grim circumstances your life lead you down this path to a powerful and old Lich it's grasp over life and death possibly persuading even the strongest of wills to its darker magic and to sign under its whims, whatever those may or may not be.

"There is only darkness for you, and only death for your people. These ancients are just the beginning. I will command a great and terrible army... and we will sail to a billion worlds. We will sail until every light has been extinguished. You are strong, child. But I am beyond strength. I am the end."
                                                                                                                                                                                                                                                                                  - The Litch; Land of Ooo

Expanded Spell List

The Lich King in it's grease allows you to choose from an expanded list of spells when you learn a warlock spell. The following spells are added to the warlock spell list for you.

Fiend Expanded Spells

Spell Level	Spells
1st	Detect Magic, ice knife
2nd	Detect Thoughts, inflict wounds
3rd	Animate Dead, Snilloc's snowball swarm
4th	Blight, sleet storm
5th	CloudKill, ice storm

Ethereal Sight

Starting at 1st level, when you reduce a hostile creature to 0 hit points, you can touch its body and look 60 feet into the Ethereal Plane or if in the Ethereal Plane, you can look back into the Material Plane. Touching the body coats it with a thin layer of frost, or partially freezes the aria that is touched.

> If the creature is not dead this deals no damage
However
> If the creature has been killed you gain temporary hit points equal to your Charisma modifier + your warlock level (minimum of 1).

Engulfing Fear

As an action the player character may cast a 20-foot-radius sphere of fog centred around the PC.
The sphere spreads around corners, and its area is heavily obscured. It lasts for the duration of 1 hour or until a wind of moderate or greater speed (at least 10 miles per hour) disperses it.
In this fog all hostile creatures must succeed on a DC 14 Wisdom saving throw or be frightened for 1 minute.
A frightened target can repeat the saving throw at the end of each of its turns, ending the frightened condition on itself on a success.

(This can be cast once per long rest)

Hands of the Lich King

Starting at 10th level, you gain the spell similar to Create Undead
With the spell components changed to V S M (A humanoid's skull carved into a bowl and filled with at least one Moonstone worth 150 GP for each corpse)

The spell uses its components upon casting and does not use a spell slot.
Use up to four gems to summon the corpses of Medium or Small humanoids within range.
Each corpse becomes a ghoul under your control. (The GM has game statistics for these creatures.) 
As a bonus action on each of your turns, you can mentally command any creature you animated with this spell if the creature is within 120 feet of you (if you control multiple creatures, you can command any or all of them at the same time, issuing the same command to each one).
You decide what action the creature will take and where it will move during its next turn, or you can issue a general command, such as to guard a particular chamber or corridor. If you issue no commands, the creature only defends itself against hostile creatures.
Once given an order, the creature continues to follow it until its task is complete.

Once the spell ends (at the end of 3 hours) the undead created disintegrate into dust once killed or when the spell ends.
This spell can be cast once per long rest, twice at 15th level and 3 times at 20th level.
These can be cast at the same time however the cost of components increases by 200GP per active use

That is not dead may come back to life

Starting at 14th level, when your soul leaves its body, it is pushed instead to a chosen container you used for the spell’s material component, this includes a range of items from a gem, crystal, reliquary, or some other ornamental container worth at least 600 gp.

While in this container, you are aware of your surroundings as if you were in the container’s space. You can’t move or use reactions.
The only action you can take is to project your soul up to 100 ft out of the container, either returning to your living body (and ending the spell and earning you a level of exhaustion) or attempting to possess a humanoids body.

You can attempt to possess any humanoid within 50 feet of you that you can see (creatures warded by a protection from evil and good or magic circle spell can’t be possessed). The target must make a CHA saving throw.

• On a success, the target resists your efforts to possess it, and you can’t attempt to possess it again for 24 hours and becomes aware that a possession has been attempted, though not whom had attempted it.
• On a failure, your soul moves into the target’s body, and the target’s soul becomes trapped in the container. 

Once you possess a creature’s body, you control it. Your game statistics are replaced by the statistics of the creature, though you retain your alignment and your INT, WIS, and CHA scores.
You keep any of your own class features but do not gain any of the creatures class features if it has any.

Meanwhile, the possessed creature’s soul can perceive from the container using its own senses, but it can’t move or take actions at all.
While possessing a body, you can use your action to return from the host body.
Returning the host creature’s soul to its body, if the host body is dead or dies while you’re possessing it, the creatures soul is taken by the death gods and promptly dies.
Upon the body you where possessing being killed you must make a CHA saving throw against your own spell casting DC.
On a success, you return to the container.
On a failure, you are killed along with the host creature.

If the container is destroyed, your soul is immediately returned to your body. if your body is dead or in a different plane of existence when you attempt to return to it, you die.
If another creature’s soul is in the container when it is destroyed, the creature’s soul returns to its body if the body is alive, otherwise, that creature dies.
You can create a new container at the same cost as before.
The container is a tough thing to break and has the equivalent of 97 hp and an AC equivalent of 17.

If you die to exhaustion you die as normal, your soul to week to enter the container.
If a healing spell brings your body back to life your soul is forcibly pushed back into your body. 
Unless possessing someone else at the time in which make a DC equal to [the level of the healing spell cast + the casters spell casting modifier]
If failed the possession ends and you return to your body.
If passed your body is preserved for 1d10 days and you are forced back into your body the moment you end the possession.