The build is Monk 16, Shadow 16. All points in Vitality.

Monk for Strength, Perfected Soul, and One Punch Monk.
Shadow for Vengeful Shadows, Thirst 2, Soul Crush, Endless Night, and Child of the Abyss.

Only gear that matters is Obsidian Dagger. Item level doesn't matter, as long as it deals shadow damage.

Enchant everything with Poison, Immortal and Evisceration.

This entire build scales everything with Vitality.

Endless Night adds 2% of your HP to your shadow damage. Soul Crush adds bonus damage based on your HP. Child of the Abyss doubles your HP.

Every instance of shadow damage benefits from the 2% damage bonus, which includes basic attacks, return damage, poison stacks, and shadow skills.

When combined with Perfected Soul, which adds 10% of your vitality to all other stats, it boosts all the stats, which is enough to turn your character into a well rounded killing machine. Currently soloing level 135, trying to farm Vitality gear.