Serpentlord

Like the serpent, a rogue keeps to the shadows and strikes when least expected. The cult of the Serpentlords have applied centuries of study to harnessing the power of serpents and turning them to their own ends. Unparalleled assassins, the Serpentlords are akin to vipers on two legs.

Fangs

By injecting a special concoction made of venom and serpent blood crafted in a ceremony known only to Serpentlords, you have grown viper's fangs. Beginning at level 3, you gain proficiency in a bite attack, which counts as a finesse weapon for you. This attack deals 1d4 piercing damage on a successful hit and you may afflict your target with Serpent Venom (described in the DMG, under "Poisons").

Bonus Proficiencies

Beginning at level 3, you gain proficiency in whips and poisoner's kits.

Loyal Fang

You have gained the trust of serpents and they see you as an ally, enough so that you may summon an avatar of serpents to aid you. Beginning at 3rd level, you learn the spell Find Familiar, which you may cast once per long rest. You may only use this spell to summon a poisonous snake.

In addition, you gain the spell Speak with Animals, which you can cast at will, but only to speak with serpents.

Camouflage Coating

Beginning at 9th level, you may blend in with your surroundings with ease as your body gains the ability to naturally camouflage itself. As long as you are wearing light armor or no armor, you may use stealth to hide even with nothing to hide behind. If you do have cover, you may make stealth checks with advantage.

Shed Skin

Beginning at 9th level, you have learned to shed your skin like old scales, leaving behind a realistic facsimile in your place. When you use your Uncanny Dodge, you may make a Stealth check against the attacker's Passive Perception. On a failure, Uncanny Dodge works as normal. On a success, you instead take no damage from the attack and move five feet in any direction as the attack strikes your shed skin. Once you use this feature, you may not use it again until you complete a short rest or a long rest.

You may not use this feature if you can not move, or there is no place within five feet where you can move to.

Beginning at level 13, you may use this feature twice per short rest.

Weapon Secretion

Beginning at 13th level, you have mastered the ability to safely secrete your natural venom onto your weapons so long as your focus is not taxed too heavily. Once per round, when you make a weapon attack that is not at disadvantage, you may apply your natural venom to the weapon before striking, adding its effects to the weapon damage on a successful hit.

Venom Transfusion

Beginning at 17th level, you may attempt to replace the venom within your venom sacs. During a short rest or long rest, you may purge your sacs of their current venom and attempt to inject yourself with any venom that you have at least one dose of. Make a DC 20 intelligence-based Poisoner's Kit check. On a success, you replace your current venom with the chosen venom. On a failure, you lose access to any natural venom for one day while your venom sacs refill. Whether or not you are successful, you may not attempt to use this feature again for one week, as you need time to heal from the procedure.