The Omni Pact

The alien being that formed an contract with you, gave you a simple task to perform, that simple task being, collecting ESSENCE samples with the gadget bestowed upon you, and as you grow in power this weapon will grow with you.

"It's strange, as it's like breathing in my hands, this alien mystical item pulsating in various colors, I can feel that It wants to attune to me, It wants me.. Is this weapon alive..?"

New User

Beginning at 1st level, The alien being bestows to you It's most powerful weapon, an strange device that shines in various colors, as you approach the item It launch's itself in your direction attaching itself in a part of your body of your choice.

As you attune with this item, you can feel It pulsating, almost breathing in your hands..
You can feel the rhythmic pulsations of this mystical alien device slowly synchronize with your heart's palpitations, you feel strange, not stronger, but strangely optimistic for the future with this weapon now permanently attached to you.. 

When attuned with this item, you gain the following benefits:
----------------------
Security System:

+2 of AC while attuned with this item, and every feat/skill/bonuses/actions/etc.. that would apply to a shield can be applied to this item, but you cannot use shields.
"You feel that strange alien power, the constant lightnings coming from the device, you feel It want's to protect you, this energy is very similar to pure magic"
===
Essence Analysis :

You can take Essence samples from creatures (that have blood or some kind energy powering then) the creature must no be dead for more than 4 hours.
After sometime [DM'S CRITERIA] an strange sound will be heard from the device, an icon, almost an image of the creature you sampled and now you understand when the being said It was a powerful weapon, as you activate this device..
"Almost in a instant, you feel all of your bones be broken, your veins be torn apart and every single cell of your body scream in pain, that 1 second was the very essence of eternal damnation.. but now your body is reformed, anew with It's new ESSENCE."

(This ability will partially function as the Wild Shape feature from the druid, but with some tweaks..
You have to use an action to transform, and the duration of the transformation is only 10 minutes, having also an limit to how many times you can transform in a specific creature, you can only transform into the same creature a number of times equal to half of your proficiency bonus.)

EXPANDED SPELL LIST
"Omni's Adaptability"

1st-  Faerie Fire / Burning Hands

2nd-  Branding Smite / Silence

3rd-  Lightning Bolt / Speak with Dead

4th-  Wall of Fire / Guardian of Faith

5th-  Greater Restoration / Antilife Shell

Upgraded Inteligence

Starting at 6th level, as you transform in the creature that you recently analyzed it's essence, you gain some additional options while you are transformed.

While transformed, if you reduce an enemy to 0 HP you can as a reaction extract some of It's essence to heal 2d6 hit points, you can use this trait a number of times equal to your charisma modifier.
additionally, while still transformed, If you have 2 or more ESSENCES analyzed, you can use an bonus action to instantly transform between one to another creature, not regaining any hit points and maintaining the current hit points and any hit points exceeding the maximum of the transformation will be considered temporary (not healable) hit points until the transformation ends or you change to another creature that has more HP, this also does not reset the 10 minute timer of the transformation.

When the duration of the transformation ends the device needs to recalibrate itself for the next two hours before being used again.

Forced Evolution

Beginning at 10th level, while transformed if you expend your action you can force the device to simulate one thousand years of evolution in seconds, although being an excruciating pain inducing experience, almost 10x worse than the normal transformations, you as a result gain the following benefits until the end of the transformation (or you be reduced to 0 HP)..

You can grant an bonus of +2 in two stats of your choice, but not the same one, example: +2 Dex, +2 Con.
Additionally you gain 10 temporary HP, but when the transformation ends as a result of forcing your body into that type of stress you suffer 2d10+Con. modifier of damage, ignoring any resistances or immunities you might have. 
If you are reduced to 0 HP with this damage, you fall unconscious and you instantly get 1 failed Death Save.

Master Control

Starting at 14th level, after all you've been through, every task, every day and night, the being that bestowed this immense power, finally tells you It's motive for creating this device, this.. weapon
You are in awe as you hear the beings motives being.. [DM'S CRITERIA]
And now you know, the purpose, the real mission, the new path that you must go If you really wish to maintain this power.
If you accept the beings conditions, It will give you the Master control of It's device, meaning you gain the following benefits:

You don't need to use a bonus action to change transformations anymore, you can do it as a free action, the duration of 10 minutes changes to 3 hours and if you expend a warlock spell slot when transforming you regain half of your max HP. 

.

.

[OPTIONAL] - THE MASTER

An optional class feature with the sole purpose of lore building and maybe adding a twist at the DM's criteria. [20th level]

.

"You feel the connection between you and this living device stronger than before.."

The very next day you wake up after reaching level 20, the alien being who granted you this device says that is now the time for you to know something, the truth.

As you wake up you have found your new purpose, the true mission is: ...[DM/PLAYER CRITERIA].

And now, when you gaze at the watch on your wrist you see something, peculiar, a new essence.

-----

 

"What you are going to do now?"

"You feel it pulsating again, more violently and you could even hear a faint sound of breathing that sends a shiver down your spine"