Keywords: boar, mmo, mob, pebble
(See the best response by Ter13.)
A lot of multiplayer games have these things called instances in which a player is teleported to a zone where NPC's may be (they do not see other players). There they can hack and slash mobs without them being affected in other instances.

How would I go about programming that on BYOND? Originally I thought about playing with the invisibility variable, though I no longer believe that's the right way to go about it.

EDIT: Sorry if this is in the wrong section. Not too sure if it would be in the design philosophy or dev help.
You should look into Map Instancing by Forum_account.
Best response
I wrote a simple phasing system on the forums a while back. You should check it out: Leoinpharoh?command=view_post&post=1468887#comment8259657
Thanks guys. I'll check those out soon.