Load up Nightfall Ch.3. In the area where you have to infiltrate the infirmary hide in the red bushes in front of the two guys guarding the entrance. There will be a guard patrolling the left and right side. When they get close enough, use your Kage ability to go invisible. Quickly walk out to the center of the brown path and hit
to make noise, then walk back into the bush before Kage wears off. The two guards at the door plus the two patrolling will walk to the center path getting close enough to blind all of them with the Shadow Grenade.