Obscuring mist (played by our friend black tentacles) is on the map. Remember the concealment rules for it:
The vapor obscures all sight, including darkvision, beyond 5 feet. A creature 5 feet away has concealment (attacks have a 20% miss chance). Creatures farther away have total concealment (50% miss chance, and the attacker cannot use sight to locate the target).
AoO's cannot occur against creatures with total concealment. Without special abilities, sneak attacks cannot occur against creatures with concealment or total concealment.