Your patron is an ancient reptilian creature of deception, cunning and treachery. His cold and rational logic doesn't account for feelings or personal interest, all that matters to him is power, acquiring it and keeping it. Above all else the Aspis cheats and lies, strike deals and break them. Few but the most experience devils and

liars can see past his coils of intricate plots. Warlocks serving the Aspis will often have the feeling that they know what their patron is up to, but it will only be an illusion. The favorite tactic of the Aspis is to uses different agents, each oblivious to the work of the others, to carry menial, seemingly useless tasks. Isolated, they seem like mundane unrelated events, but once the final piece is set the grand plan unravels with a terrible efficiency. It's then too late to stop it. The Aspis usually favors reptilian creatures as his servants, such as Yuan-Ti, Naga and Lizardfolk, but it values just as much the insidious potential that can be provided by intelligent humanoids.

To name a few possibilities, your patron could be Apep.

Sseth, Nahash "the Snake in the Garden", Yig "the Father of Serpents" or a Yuan-Ti Anathema.

Forked tongue

Starting at ist level, the cold and practical logic of your patron shapes your own mind and connects you to the reptilian world. You gain proficiency with the Deception skill Additionally you can hiss to talk to and understand snakes and reptiles like if you were under a speak with animals spell When you use this feature your tongue becomes forked.

Sinuous body

Beginning at 6th level, your patron grants you with the ability to pass trough any opening large enough to fit your head. The rest of your body shrinks to fit the space and you move the way a snake would until you reach a space big enough to contain your whole body. Any movement made this way is considered difficult terrain. Additionally your gain advantage to Strength (Athletics) and Dexterity (Acrobatics) checks to escape from a grapple and can use the Escaping a grapple

action as a bonus action.

Skin of the betrayer

Beginning at 10th level, your mind and body are beginning to closely resemble that of the Aspis. As an action you can observe a creature within 30 feet, your eyes become serpent-like while you do so. The creature must make a Wisdom saving throw against your Warlock spell DC. If the creature fails, you gain the ability to shed your skin to take the appearance of that creature. Using an action you can turn into that creature, shedding your own skin and leaving an empty husk behind. You look exactly like the creature you imitate, including height, weight, facial features, sound of your voice, hair length, coloration, and distinguishing characteristics. You can make yourself appear as a member of another race or sex, though none of your statistics change.

You can't transform as a creature of a different size than you, and your basic shape stays the same; if you're bipedal, you can't use this feature to become quadrupedal for instance.

You can maintain the skin for 8 hours, after what you shed back into your own, leaving another fleshy husk behind. If you target another creature with that power you lose the ability to transform in the previous one. Any equipment you are wearing or carrying isn't transformed While transformed the Aspis hisses answers in your mind:

• You double your Proficiency bonus in Charisma (Deception) to impersonate your target and gain advantage on that roll
• You cannot be targeted by any divination magic to determine if you are telling the truth.

Once you use this feature, you can't use it again until you finish a short or long 

OPHIDIAN INFESTATION

At 14th level, your patron has invested you with his venomous grace. You may, as an action, attempt to poison a creature that you can see within 60 feet of you. The creature must do Constitution saving throw against your Warlock Spell DC. In case of failure the creature is poisoned for 1 minute. While poisoned the creature takes 4d6 poison damage at the beginning of its turn. A poisoned creature can attempt a new saving throw at the end of its turn, ending the poisoned condition on a success. Additionally the creature vomits a Scion of Aspis. The Scion of Aspis appears in an unoccupied space adjacent to the creature. The snake disappears when drops to 0 hit points. The creature is friendly to you and your companions for the duration. Roll initiative for the snake, which has its own turns. It obeys any verbal commands that you issue to it (no action required by you), If you don't issue any commands to the Scion of Aspis, it defends itself from hostile creatures but otherwise takes no actions.

Once you use this feature, you can't use it again until you finish a long Rest