So here is the scenario. My group triggers a trap in a 30X30 room. This bars the door they came in and opens a secret door with a dwarf in full plate + tower shield whose only job is to block the corridor. Now the room is starting to tilt which in turn will drop the PC's (and ambassador they are protecting) into the room below.
The sorcerer casts (gasp) hideous laughter and my tank drops prone. According to the rules to get past a non-helpless opponent the party needs to either tumble or overrun according to the rules on page 193 of the core rulebook. The players thought that because the target was prone it would make it easier but the rules are pretty clear as far as I am concerned.
What do you guys think or did I miss another rule somewhere?
The Acrobatics DC is the opponent's CMD. Keeping in mind under the desc. of CMD (p.199) the line "Any penalties to a creature’s AC also apply to its CMD".
According to the Prone condition: A prone defender gains a +4 bonus to Armor Class against ranged attacks, but takes a –4 penalty to AC against melee attacks.
As this movement is concerning threatened squares (ie. melee) he has a -4 penalty to his CMD. Or in other words they get a +4 bonus on the Acrobatics/Overrun check.
Depending on how much time you have, there are a couple of other options to consider. Assuming you have some poor CMB characters who might not be able to get past the laughing dwarf, but at least one very good CMB character, that one could go first and try either:
1) Grapple: with the minus to CMD and no action available to attempt to break the grapple, this is a great two-round solution. On the second round, either move the dwarf out of the way or pin him so you can move past him freely.
2) Bull rush: push the dwarf out of the way. Enough said.
Another thing to keep in mind is that while the dwarf is affected by Hideous Laughter he can't take any actions so if the sorcerer has enough space that he/she can simply move through a "threatened" square the dwarf can't take any attacks of opportunity. With that little caveat, +1 to the above posts.