As a reaction, which you use when you are hit by an attack or missed by 4 or less, poison bursts from your skin. If the creature who damaged you is within 10 meters, it must make a Reflex saving throw.
On a failure, it takes 4d6 poison damage.
On a critical failure, it takes twice as much damage.
On a success, it takes half as much damage.
On a critical success, it takes no damage.
You can increase the damage by 4d6 for each additional mana expended.