1) Go down stairs with Sword of Nex on you
2) Toss any item at door - door will open
3) Toss any item at demon face - teleporter will be activated
4) Throw bomb or shoot arrow through teleporter (look at experience bar to confirm hit)
5) Wait a bit so monsters can move and repeat step 4. Do this a few times. You can toss all your stuff through the teleporter if you want to (makes it hard to pick up the arrows, though

)
6) You should have done some serious damage now. Run through teleporter, hit forward key and let those weapons swing until you hit the wall (don't forget to pick up arrows or whatever your favorite throwing/shooting weapon was)
7) Now you're at the wall, meaning monsters can only attack you from 3 directions. Plus, you've already killed some of the stuff
8) Fight your way to your corner of choice
9) Lay waste on the rest and knock yourself out looting