Stunning Strike

Once per turn when you hit a creature with a
Monk weapon or an Unarmed Strike, you can
expend 1 Focus Point to attempt a stunning strike.
The target must make a Constitution saving throw.
On a failed save, the target has the Stunned
condition until the start of your next turn. On a
successful save, the target's Speed is halved until
the start of your next turn, and the next attack roll
made against the target before then has Advantage.