Viper

Vipers are deadly rogues who emulate the patience, precision, and lethal venom of serpents. Whether trained as assassins, poisoners, or hunters of dangerous prey, these rogues strike swiftly and without warning, debilitating their foes with carefully prepared toxins before slipping beyond retaliation. As their mastery grows, Vipers learn to concoct increasingly potent venoms and deliver them with deadly efficiency, ensuring that even those who survive the initial strike soon succumb to its effects.

Level 3: Serpentine Lethality

You've learned to emulate the agility and deadliness of snakes. You gain the following benefits.

Coils of the Serpent. You can use Dexterity to attempt a Grapple, and you can Grapple without needing a free hand. In addition, you have advantage on Dexterity saving throws made to avoid or end the Grappled condition.
Fangs of the Serpent. When you use Steady Aim, your Speed is not reduced to 0 if you are only wielding weapons with a d4 damage die, such as daggers or sickles.

Level 3: Venomous Strikes

You gain proficiency in the Poisoner's Kit, and you can use abilities and attempt checks that require a Poisoner's Kit even when you do not have one. In addition, when you deal Sneak Attack damage, you can change the damage type of the Sneak Attack's extra damage to your choice of Acid or Poison damage.
Additionally, you can craft poisons in half the usual crafting time and at half the usual cost.

Level 9: Toxic Adept

Your mastery over poison has granted you the following benefits.

Poison Resilience. You gain resistance to Poison damage and advantage on saving throws to avoid or end the Poisoned condition. 
Potent Venom. When you use the Poison option of your Cunning Strike feature, the target has disadvantage on all saving throws against the Poisoned condition inflicted by the ability. In addition, Acid and Poison damage you deal ignores resistance.

Level 13: Lethal Additives

When you deal Acid or Poison damage with a Sneak Attack, you can apply one of the following effects to the target of the Sneak Attack.

• Anticoagulant: The target of the attack takes 1d8 extra Piercing damage, and at the start of each of its turns for 1 minute it takes an additional 1d6 Piercing damage unless it recovers any Hit Points.
• Necrosis: The target of the attack takes an extra 2d6 Necrotic damage, and it can't recover Hit Points by any means for 1 minute,
• Neurotoxin: The target of the attack takes an extra 2d4 Psychic damage, and it must succeed on a Constitution saving throw against your Cunning Strike save DC or be Stunned until the end of it's next turn.

Level 17: Apex Toxin

As a bonus action, you can apply your most potent poison to a weapon you are wielding that deals Piercing or Slashing damage. For 1 minute, the weapon deals an additional 4d6 Acid or Poison damage on a hit, and targets hit by an attack with the weapon gain the Poisoned condition for 1 minute. You can do this once, regaining expended uses of this ability upon a Long Rest.