Can any combat maneuvers be attempted by a prone character?
If so, which ones, and what are the modifiers for that situation?
What combat maneuvers can be attempted on a prone creature?
What modifiers apply?
Can any combat maneuvers be attempted by a prone character?
All of them, but there will be limits (especially on movement) based on your prone condition. For example, Drag will be limited because your prone movement is limited, as will bull-rush and overrun. You can only crawl 5 feet as a move action while prone (unless you have a particular rogue talent or other special exception).
If so, which ones, and what are the modifiers for that situation?
Rules: "A prone attacker has a –4 penalty on melee attack rolls and cannot use a ranged weapon (except for a crossbow)."
Rules: "When you attempt to perform a combat maneuver, make an attack roll and add your CMB in place of your normal attack bonus. Add any bonuses you currently have on attack rolls due to spells, feats, and other effects."
A melee combat maneuver is an attack roll. Being prone is an example of 'other effects'. There are a scant few maneuvers that can be done at range under special circumstances, so those are right out.
What combat maneuvers can be attempted on a prone creature?
Anything except trip. Some say you can even attempt a trip against a prone target, but that it will have no effect even if "successful".
What modifiers apply?
Rules: "A prone defender gains a +4 bonus to Armor Class against ranged attacks, but takes a –4 penalty to AC against melee attacks."
Rules: "Any penalties to a creature's AC also apply to its CMD."
What combat maneuvers can be attempted on a prone creature?Anything except trip. Some say you can even attempt a trip against a prone target, but that it will have no effect even if "successful".
You can "trip" a prone target if you're using a seven branched sword. It will add the flat footed condition to the prone condition.
I can't find any rule that would stop a prone human from bull rushing an Ogre by pushing against his knee.
It would even make a good tactic to bull rush an other non large/reach monster and stand up (if you have improved bull rush). Personaly I really dislike it because it doesn't make sense to me. When I think of a bull rush I see a shoulder or shield bashing the enemy away, which you can't do prone. But yes, I think it's legal
Overrun would normally be imposible because of the five foot crawl speed.
Overrun would normally be imposible because of the five foot crawl speed.
True, but there are ways to have a greater than five foot crawl speed