Dagger is mundane until attuned. Transforms into a blood red dagger that glows. Looks like a normal dagger to everyone else.

Upon attunement the dagger speaks to the wielder, telepathically. A demon named Vorthas has been trapped in the dagger and he gives the power. 

Wielder gains 5% chance to kill a target they have hit.

A critical hit doubles the percentage.

Automatically hits first attack against a creature when hidden

After every failed use the percentage to instant kill goes up by 5%. Resets when used.

Wielder can creature shift (They can possess creatures) However however much hp the enemy has is how much it would cost to shift into there bodies

Notes: Damage: Necrotic, Finesse, Light, Thrown