Once per battle, deal ongoing damage to a target you hit with a natural even attack roll as a free action. The ongoing damage equals 5 times your level. (For example, at 3rd level you would deal 15 ongoing damage against a single target.) As usual, a normal save (11+) ends the damage. A critical hit doesn't double this ongoing damage.
Once per day, you can instead use cruel to deal 5 ongoing damage per level against an enemy you miss or that you roll a natural odd attack against.