Just did this solo...

Pass the toad on the first left into the area, loop around up to the second level and WAIT for the spriggan to patrol up and away, then walk to the clearing to the left and wait for the spriggan to pass again, and walk onto the bridge, get to the end and wait for the next spriggan to walk up and away, following behind him.

At this point you can easy get to turning leaf and then to the box.