The First Anathema

Your patron is the first and most powerful breed of Yuan-ti; an anathema.

The anathema are pure-blooded Yuan-ti that desire nothing more but to extend the reach of the Yuan-ti and to deprave the unworthy of magic capabilities. Your patron is the first anathema, with power that far exceeds that of it's descendants.

You may be in this pact as a result of a transformation into a Yuan-ti, a desire for power/hatred of magic, or a shared desire with the anathema. 
You may be granted additional power as you grow accustomed to your Yuan-Ti form or you are given power by your patron for granting their desires.

Expanded Spell List

The Yuan-Ti's influence 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.

First Anathema's Expanded Spells

Spell Level	Spells
1st	"dissonant whispers""ray of sickness"
2nd	silence, "tashas mind whip"
3rd	slow, nondetection
4th	"vitriolic sphere", polymorph
5th	cloudkill, greater restoration

Magic Resilience

Starting at 1st level, when you or a creature you can see is targetted by a spell attack roll or spell saving throw, you may use your reaction to reduce the attack roll or spell save dc by your charisma modifier.  You may use this feature after seeing the outcome of the dice. You may use this feature a number of times equal to your proficiency bonus, regaining all uses after a long rest.

Acidic Blast

If you know the cantrip eldritch blast, it deals acidic damage instead of force damage.

Serpentine Scales

Starting at 6th level, Your patron changes your natural skin to a set of scaled skin of your choice.

Armored Scales

Your unarmored ac becomes 14 + your dexterity modifier.

Chameleon Skin

You have advantage on stealth checks that rely on sight. Additionally, you gain the ability to hide when unobscured, but lose advantage on stealth checks.

Yuan-Ti blood

Starting at 10th level, if you are resistant to poison damage you now become immune. otherwise, you gain resistance to poison damage. You also can no longer become poisoned.

Enhanced Poisons

Starting at 14th level, when you deal poison or acid damage, you overcome poison and acid resistance of the target. Your targets have disadvantage on saving throws to avoid the poisoned condition.

Additionally, when you deal poison damage to a target, you may change the damage type to acid, or, when you deal acid damage to a target, you may change the damage type to poison.