The Demon Lord

You either struck a deal with a demon lord, or became one yourself.  Either way doesn't matter now that you have become all powerful.  Versatile and unpredictable, you strike your foes down with cunning skill, or charm them into madness.  You are a god, and no one will get in your way, not even morals.  Evil, mischievous, or revenge seeking, these are key traits to Demon Lord Warlocks.  Some, insane, others, evil.  But none of that matters, you are a force of power, meant to murder and mangle.  Enjoy the power you were given, it's a rare gift.

Growing Power

You gain a multitude of abilities that you can level up every 3 levels.  Every 3 levels, you upgrade 3 chosen things once.  abilities that don't grow stack(Ex.you gain a +1 to attacks and a damage increase the next level.  You still keep the +1 and the damage).  All abilities max out at 4

Wings of the Fiend: you gain wings that give you the power of flight. 0: you have nubs.  1: you gain small wings, you take no fall damage as you glide.  2: you grow medium wings, 30ft flying speed.  3:your wings expand to a large size, 60ft flying speed.  4: your wings cloak the day in shadow, You can, 3 times per short or long rest, use 20 feet of flying speed and deal 2d8 force damage to one hostile creature within 10 feet of your take of area and you take no attack of opportunity.

Horns of the Demon General: You grow horns stronger than steel.  0: you have small horns the size of a baby goat.  1: you grow horns the size of a mountain goat, if you move 30 feet into someone, they take 1d6 bludgeoning damage.  2: you have horns that beat a ram,  if you move 30 feet into someone, they take 2d6 bludgeoning damage.  3: Your horns are like a young dragon's, if you move 30 feet into someone, they take 3d6 bludgeoning damage. 4: your Horns rival that of Baphomet's, when you move 30 feet into someone, you deal 5d6 force damage.

Eyes of the Fire Judge:  You can see straight through people.  0: you have eyes that have a very faint glow.  1:  Your eyes glow and you can judge more easily, you have advantage on insight checks to see if people are lying.  2: Your eyes glow a fiery glow and you see the lies in people, you gain expertise in either insight or perception(your choice).  3: Mortals can't lie to you, you see through them,  Mortal creatures have disadvantage on lying to you.  4:  You have seen the ends of the abyss and it's cold and inhospitable environment, you have 20 ft of truesight. 

Claws of the Devil: you grow claws of pure power.  0: Your nails are always sharp.  1: Your nails become short claws, your unarmed strike now deals 1d6 slashing damage.  Your claws become even bigger and sharper, you can now cut medium tough things like wool, cloth, and leather, if you attack someone wearing leather armor that isn't rare or higher in rarity, it is torn and for each attack, they get a -1 to AC.  3: your claws become like that of a sword in sharpness, your unarmed strike becomes 1d8 slashing damage.  4: your claws are sharper than a greatsword, your unarmed strike becomes 1d12 slashing damage.

Arcana of Avernus:  You become really magically talented as the power of avernus fills you.  0:  You can make a small firework to impress people.  1: you can cast knock once per short rest.  2: you have a +1 to all spell saves and spell roll to hits.  3: you can cast spirit guardians once per short rest. 4: you can cast creation once during a short rest

Extra Attack

You can attack twice instead of once

Hide from Mortal Eyes

Until hit, you and your actions become imperceivable to any mortal.  Instead, the mortal being will see their own version of what you are doing.  This type of action they perceive always looks like a good thing.

Hellish Bombardment

You use a flurry of blows to strike down your enemies.  Once every short or long rest, you can imbue an attack with this ability.  When you use a weapon attack, you deal an extra 11d10 fire damage.  If you attack with a spell it deals 11d10 force damage.  If you reduce someone's Hp to 0 with this, they are either incinerated if its fire damage, or blasted to bits if it's force damage.  The soul of the victim is sent to your patrons lair and can't escape.  If you attack with both a spell and weapon attack, you deal 10d10 of any damage and the target is deafened.

Hex Warrior

You can imbue a number of weapons equal to your constitution modifier plus your proficiency bonus.