Overrun should work, although for some obscure reason incorporeal creatures in the bestiary don't seem to apply their strength penalty to their CMD?
Edit: It seems like they add their dex modifier twice instead, which typically results in an obscenely high CMD for something without any physical form
Lacking a score entirely (-) means no modifier at all (mathematically the same as 0), unlike a score of 0 (which means a modifier of -5).
Now let's break down the CMD of a Shadow. It gets +2 for its BAB and +2 for its DEX (it has no STR modifier, so nothing to add), which takes us to 14. It also has a +2 deflection bonus (based on its CHA) and a +1 dodge bonus. That brings us to 17, its listed CMD.
The CHA-based deflection bonus does not replace STR in the CMD. It applies to AC and CMD because the rules say so (like the dodge bonus).
Also, since an incorporeal creature cannot be moved at all by corporeal creatures, it's immune to most combat maneuvers (even overrun is suspect, since a high roll allows you to knock your target prone). Dirty Trick might work, but I wouldn't bet on it. That leaves stuff like Acrobatics DC to avoid AoO's.
edit: You are correct. I didn't even read your entire post the first time. I apologize. I forgot that it applied as a deflection bonus.
What helped me get it wrong-->I read somewhere that an incorporeal creature that wants to use a strength based check defaults to charisma, if that situation somehow happens. I can't remember where though.
The question would be if a creature without a body still occupies a square. So far I ruled they don't, but I can see other GMs rule otherwise. In any case I would assume that they can't try to stop an overrun maneuver as they can't take "any physical action that would move or manipulate an opponent". Blocking the path would likely fall into that category.
|The Black Bard|
Much like how Gelatinous Cubes can't be tumbled through with acrobatics, I've ruled incorporeals as being one of the "listed exceptions" to the base movement rulings. I am probably being overly generous in my interpretation since I allow them to pass through creatures as well as other non-animate objects. Attacks of opportunity still apply.
This lets me:
1. Give the classic Ghostbusters treatment, which really seems to pleasantly annoy my players/PCs. "He slimed me!"
2. Allow narrow hallway fights to both be more dangerous but more participatory for the PCs, as incorporeals occupying PC squares get cover bonuses but can be attacked by most of the party.
3. Witchfires. Their curse is on contact. Flying through the entire party on the first round to potentially give all the PCs 50% more fire damage? Amazing. With 2 or more witchfires? Brutal.