Warlock Pact: Student of Caiphon

Warlocks are often born out of seeking forbidden knowledge, or some great tragedy that had befallen them, and a powerful being taking advance.  A mote of power, in exchange for eternal servitude and damnation.  Perhaps you were seeking a way to right a wrong.  Perhaps you simply wanted knowledge that was kept from you.  In either case, when you reached out, something answered.

Dreaming of an endless purple sea of flame, watching over a heaving maw that whispered secrets.  Secrets that required sacrifice.  Namely yours.  Throwing yourself into the star, you were consumed by it, and when you woke you found you were changed.  New knowledge was within your mind, secrets uncovered.  And your eyes now became a purple hued, marking you as an emissary and student of the Dream Whisperer.  Ever new knowledge crosses your mind every day, and it's up to you to keep track of it before it consumes you completely.

Caiphon's Guidance

Starting at level 1, Caiphon's whispers have given you insight on lost knowledge.  You gain Proficiency and Expertise in Arcana and Religion skills.  In addition, when you reduce a hostile creature to 0 hit points, you gain a +1 bonus to your next skill check roll until you take a short or long rest.

Expanded Spell List
When choosing Student of Caiphon, you gain additional spells that do not count against your maximum number of spells known.

1st         Identify, Divine Favor
2nd        Crown of Madness, Detect Thoughts
3rd         Daylight, Hunger of Hadar
4th         Sickening Radiance, Confusion
5th         Commune, Dawn

Fevered Certainty of Caiphon

Starting at level 6, you are able to sacrifice a portion of yourself for the price.   Once per Short or Long rest, you are able to roll a skill check or saving throw with advantage.  After doing so, whether you succeed or fail, Caiphon takes it's due, dealing 10 radiant damage that can't be reduced in any way.

Stair of Light

At level 10, once per long rest, you are able to conjure a stair of light.   The Stair of Light can be mounted by the warlock and any willing creatures after conjuring it, and acts as a teleport spell.  When mounted, the warlock can choose a specific location, or simply not choose allowing the DM to select a random destination for the individuals mounted.   At the end of the teleportation, the warlock and each creature who mounted the Stair of Light must make a DC 15 wisdom saving throw.  On a failure, the creature suffers from Short Term Madness.  If they failed the saving throw by 5 or more, it becomes Long Term Madness instead.  

Emissary of Caiphon

At 14th level, you are given the powers as an Emissary of Caiphon.    You gain the following benefits.
-Gain an Aura of Madness, causing creatures to glimpse the horrors that you have become accustomed to.  You gain an aura of 15 feet, creatures of your choosing in the aura are subjected to maddening whispers, forcing them to roll a 1d4 on all saving throws and reducing the save by that amount.
-Gain Resistance to Psychic and Radiant damage.
-Gain the ability to hear the prayers to Caiphon, and their relative location compared to your own.  
-Gain advantage on Charisma checks and saving throws when dealing with Star Spawn.