We have six DMs sitting around a table. It usually goes something like this:
DM1: Okay You're walking down the corridor when a group of 4 bugbears comes into view around the corner.
DM2: Which side of the corridor - show me on the battle mat (DM1 complies) Ha! The Lurker Above above drops on heir heads-
DM3: How long was it lying in wait ther?
DM2: two weeks--
DM3: HA! the Lurker is already dead because a band of adventurers set off a poison gas trap here last week.
DM4: What!?? Lurkers Above are immune to poison!
DM5: No They're not - doesn't say that here!
DM6: Well of course not - That's DM3's converson of the Lurker Above. Look at mine.
DM5: Okay, I'll go with the poison immunity, but CR4, what were you thinking? In any case my DMPC ranger attacks the lurker with his two scimitars. He hits AC 17 with the first swing and AC15 with the second.
DM1: No you don't; you miss both times - the variant ranger doesn't get two weapon fighting...
etc.