The Servant of Secrets

Drawn by the mysteries of this world, you have made a deal with a patron of coveted information and dirty mistakes. A Patron who knows all and sees all. 

You as the subject of lesser information know not the name or face of your Patron. 
(For your Dungeon Master's Sake, your Patron is a variety of misshapen creatures or a creature with a misty face. The best and easiest is Vecna.) 

Expanded Spell List

The Patron of Secrets lets you 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.

Servant of Secrets Expanded Spells

Spell Level	Spells
1st	Detect Poison and Disease, Identify
2nd	Augury, Detect Thoughts
3rd	Clairvoyance, Speak with Dead
4th	Arcane Eye, Locate Creature
5th	Commune, Rary's Telepathic Bond

Insightful Servant

Starting at 1st level, your basic understanding of body language and vocal inflections increases with your Patron's deal. You automatically gain expertise insight checks. 

[ Expertise: Your proficiency bonus is doubled for any ability check you make that uses the chosen proficiency. ]

The Servant's Share of Secrets

Yearning for more knowledge and skills, you reach out to your patron in hopes of an answer or a gleaming of useful information. 

These skills dissipate at the end of a long. At which point you may try to reach out to the Patron again, but there is only a 25% chance of them responding.

(When you use this feature, the DM gives you extra proficiency in two skills as well as a saving throw. You must either accept the set in it's entirety or deny it.)

[ This transition can only be requested once a sacrifice has been fulfilled for your Patron. Talk with your DM about this, but usually it will be something against what your character would normally do. ]

Mystic Arcanum (5th Level)

At 10th level, your patron bestows upon you a magical secret called an arcanum. Your DM chooses one 5th-level spell (that fits your character) from any spell list as this arcanum at the end of each long rest as long as you are in good graces with the Patron.

You can cast your arcanum spell once without expending a spell slot. You must finish a long rest before you can do so again.
All future Mystic Arcanum's happen in the same way as this one.

At higher levels, you gain more warlock spells of your choice that can be cast in this way: one 6th-level spell at 11th level, one 7th-level spell at 13th level, one 8th-level spell at 15th level, and one 9th-level spell at 17th level. You regain all uses of your Mystic Arcanum when you finish a long rest and can receive new spells as long as you are in good graces with the Patron.

Servant's Knowledge

You have advantage on absolutely any Mental Skill Check, but not saving throws. 
However, doing so gives you a task to fulfill by your Patron (Determined by your DM) before you can use this advantage again.