Enter(mob/M)
usr.loc = locate(/obj/hoix7)
usr.y-=1
return..()

This is attached to a turf. Why would this take me to a black screen instead of where it took me before?

• No put usr in proc. Duh!
• You apparently want this to do something when entering a turf, but you've used the wrong proc entirely. That should be Entered(), not Enter().
• If your locate() succeeds, it will return an obj, not the turf it's on.
• If the first /obj/hoix7 found is at a null location, then trying to change y will do no good.
• Just for future reference, you should take extra tabs out of your code when you post it. Each line has about 3 too many tabs before it. It's a good idea to put <dm> tags around your code, too.
  
  The correct code would probably look like this:

Entered(mob/M)
  if(ismob(M))
    for(var/obj/hoix7/O)
      if(O.y>1)
        M.loc = get_step(O, SOUTH)
        return