As an action, you can make a melee weapon attack that deals slashing damage in an attempt to cripple the creature. Add the stamina die to the attack’s damage (add half if you miss by 4 or less). On a hit, the creature must succeed on a Fortitude saving throw or it is slowed 1 for the duration.
A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.
You can increase the damage for each additional stamina die expended and the slowed level by 1 for every other additional stamina die expended.