That must be a Swiss Army sword.

Obviously, if the fairies live among us, there have to be times when they work their magic away from our eyes. What we see here is Malachite taking those few preparations necessary to ensure that humans don’t walk down the alleyway while he does his work.

There are more certain methods of doing this, of course, but he has to be careful not to seal the alleyway off from the traces and essences that he’s actually going to be looking for. After all, he is effectively hunting for Keith, now. It does no good to give a dog the scent if you lock him in a hermetically sealed room.

Of course, the question could be raised — how did he know where to find Keith in the first place? In fact, the question was raised over on the forum. The answer, of course, is that he didn’t. Another fairy — a seer, like Mercy (perhaps Mercy herself) found the human who saved Sonata’s life and divined what happened. Malachite was then dispatched to take care of giving the kindly human his boon and seeing his life end with as little fuss as possible. Which, as you already know, didn’t work out.