It would appear I need more practice at telefragging shopkeepers...
...but whatever gets the job done.
If it's too fast to figure out what's happening, here's a step by step:
I checked below, lined up with the shopkeeper
Jumped one block and held down on the control stick
Fired off the teleporter
This placed me one block up, i.e. right above his head knocking him out (Had I not jumped I probably would have done it right)
So what do I do? I decide to run to the right instead of leaving. For no reason at all
I then turn around and teleport back hoping to get him a second time just as a bullet flies over my head and a bat wakes up behind me
After teleporting behind him I land on the ledge just as he runs up and tosses me into the air over the door
Knocked out I pick up some gold, but I wake up just in time and wait on the other ledge
He jumps over me as I run under but I hit the bat that narrowly avoided the bullet from before which puts me in sync with the shopkeeper
I end up landing on his head after a jump while in sync with him knocking his shotgun out of his hand
I run to grab the shotgun but get a skull instead, then pick it up and fire it off before he can get to me again
One more shot and he's done
The whole time I didn't get hit by a single bullet. I did lose a heart from him throwing me.