Yoshiki Akita (Human Monk 3)
Yo maintains his position against the wall on the side of the staircase, staying out of sight to anyone coming up the stairs. He gestures for everyone to get back out of view.
If no one says anything, stays hidden, and the man below walks up unaware, Yo will leap out and attempt to grapple the man as soon as he comes into view, hopefully catching him flat-footed.
CMB +7 (I'll wait on rolling to avoid biasing other people's actions)