School of The Viper

Description
One of the southernmost offshots of the witcher caste, it was probably the most alien and secretive.[4] The Vipers managed to collect an incredible collection of books and scrolls on the Wild Hunt, leading some of its members to speculate whether their school was founded for the very purpose of solving the riddle of the spectral riders.

The Vipers were trained on twin small blades and an assassination-based approach to killing monsters. Their fighting style featured sinuous, unpredictable movements using the two blades ("fangs").

For source and more see: The Witcher Wiki

Class Features
Proficiencies: armor (light), weapons (martial, simple)

Skill points: 4 + int modifier ( (4 + int modifier) * 4 at 1st level)

Skills:  Athletics, Animal Empathy, Craft Trap, Heal, Intimidate, Knowledge: Chaos, Knowledge: Runes and Glyphs, Knowledge: Nature, Knowledge: Monsters, Perception, Persuade, Ride, Stealth, Survival, Taunt

Primary saving throw(s): Fortitude and Reflex

Base attack bonus: +1/level

Spellcasting: Signs

Witcher knowledge

 * Starting at 1st level, a Witcher adds their class level to knowledge checks for monsters.

Viper Style

 * Witchers of the school of the Viper wield a pair of blades not unlike the fangs of a snake. They gain the Two-Weapon fighting feat at level 1.
 * At 8th level they gain the ability to cast signs while there is a weapon in their offhand (but not other objects such as a shield or torch).

Viper Strike

 * This ability functions the same as a rogue's sneak attack.

Deflect Arrows

 * At 12th level, a Witcher gains the deflect arrows feat. Note: This feat does not function if there is a two handed weapon equipped, or anything in the offhand.

Blinding Speed

 * A Witcher of 20th level gains the blinding speed feat.

Trial of the Grasses
After completion, the Witcher unlocks the ability to progress past level 9 in addition to the following bonuses:
 * +2 to Strength, Dexterity and Constitution
 * Low-Light Vision
 * Resist Disease
 * Resist Poison
 * Still Mind
 * Improved Initiative
 * Can consume Witcher Potions

Signs
The Witcher gains the ability to cast signs, which improve with Witcher level. A Witcher can use this feat once per minute. The DC of the signs is 12 + 1/2 the Witcher level. A witcher can only cast a sign while wielding nothing in the offhand or using a two handed weapon.

All the signs except for Quen share a cooldown.
 * Aard: Fortitude save or be knocked down. instant cast.
 * Igni: Deals 1d4 fire damage per Witcher level in a cone. Instant Cast.
 * Quen: The Witcher gains a shield against all forms of damage. This blocks 5 damage per Witcher level before expiring.
 * Yrden: Places a magical trap on the ground for one minute. When Triggered slows the target for 1 round per 5 Witcher levels.
 * Axii: Charm Monster