Viper

The Viper
Rogues of the wilds learn to survive in harsh environments that men and women weren't meant to live in. Some take up the druidic arts to better mesh with the land, and those rare few are known as Vipers.

Viper Strike
Masters of poison, Vipers conjure up wicked venoms and toxins with startling ease. At 8th level, the Viper can choose to treat their sneak attack damage as poison damage. If they do so, they gain access to several options to modify their sneak attack. These options reduce their sneak attack bonus damage to add special effects. A Viper must deal a minimum of 1d6 damage on their sneak attack, but can choose multiple effects. For any save DCs, the Viper uses 8 + Proficiency Modifier + Their Dexterity modifier, and those that inflict conditions have the targets make a save at the end of each of their turns unless stated otherwise. The following options are not initially available but can be accessed at level 9, when sneak attack increases to 5d6.
 * Blinding Poison: This effect costs 3d6 sneak attack dice. The target of the attack must make a Constitution save or be blinded.
 * Caustic Toxin: This effect costs 2d6 sneak attack dice, allowing the Viper to ignore poison resistance or immunity on a target. In addition, the target must make a Constitution save or have their resistances and immunities to poison stripped.
 * Cloying Venom: This effect costs 1d6 sneak attack dice. The target of the attack must make a Constitution save or be poisoned.
 * Killing Venom: This effect costs a minimum of 1d6 sneak attack dice. The Viper chooses how many dice to spend, up to a maximum of one-half their maximum dice (round down). The target of the attack must make a Constitution save with disadvantage on this initial save if they are poisoned. If they fail, at the start of each turn they take the amount sacrificed plus an additional 1d6 in poison damage.
 * Psychoactive Poison: This effect costs 3d6 sneak attack dice. The target of the attack must make a Wisdom save or be charmed or frightened (Viper's choice).
 * Anti-Coagulant: This effect costs 4d6 sneak attack dice. The target of the attack must make a Constitution save or gain vulnerability to bludgeoning, piercing, and slashing damage.
 * Neurotoxin: This effect costs 4d6 sneak attack dice. The target of the attack must make a Constitution save or be paralyzed.
 * Sedative: This effect costs 4d6 sneak attack dice. The target of the attack must make a Wisdom save or be affected as the Slow spell.

Poison Haze
The Viper strikes quickly, hides, and then strikes again, inflicting more and more of their venoms on foes. At 13th level, when the Viper spends their Cunning Action to Hide, they gain advantage on the check against creatures who they have afflicted with one of their Viper Strike effects. When they use the Dash action with their Cunning Action, any creatures that are under the effects of their Viper Strike take disadvantage on their next save against the effects, if the Viper moves adjacent to them during the movement. When they use the Disengage action with their cunning action, they leave behind a cloud of poison in a 10' radius from the space they left that deals 2d6 poison damage to creatures who end their turn inside of it. The cloud disperses at the start of the Viper's next turn.

Deadly Toxins
The Viper's toxins only get deadlier with time and research into the vicious ravages nature creates. At 18th level, the Viper deals d8s for their sneak attacks against any creature who has one or more of their Viper Strike effects afflicting them. This increases to d10s for a creature afflicted by two Viper Strike effects, and a maximum of d12 for three Viper Strike effects.