I was going to make a new thread for this but since it is somewhat related...
Scenario in a nutshell: Party exploring underground section of a tomb, where they find some brown mold completely blocking their way into a room. They all run across it, everyone takes damage. Warlock gets staggered at the edge, everyone else makes it across.
While split up, the group accidentally awakens a Medium earth elemental, and the lurking strangler who heard their bumbling about was waiting in ambush here. The latter didn't do anything though as all of its attacks were resisted or missed entirely.
Warlock attempts to heal himself, botches the UMD roll on a lesser vigor scroll spectacularly and KOs himself.
Everyone else deals with the elemental. They get it down to 3 HP, and are doing fairly well. Then the druid, who had barely been paying attention all fight casts Obscuring Mist. This completely screws up the strategy, and blocks a reach True Strike AoO that had a 95% chance of ending the encounter because total concealment = no AoOs.
Slam attack, down goes the Duskblade.
Cleave, down goes the Favored Soul.
Cleric attempts to melee, misses quite awesomely.
Slam, down goes the cleric.
Druid's summoned pet goes for what would be one last attack...
Natural 20, beats concealment. Max damage, and rolled openly.
So he revives them all who are quite relieved. Except the warlock. Unbeknowst to them, the strangler decided that since it couldn't do much in the fog, it'd just fly out and hide. Then it sees the lovely target... who is dead. They don't know that yet.
Cleric attempts to run across the mold again to save him, and staggers himself.
I have the strangler hiding over there so if he does make it, it will readied action Cause Fear to try to scare him back into the mold (and KO him)
The way things are going, I may very well kill 5 ECL 3 characters with a stock CR 1 monster, and an environmental hazard they haven't figured out to hit with cold yet. It was pure luck the elemental didn't do it.