Marco Fiero:
Even if momentum is enough to keep the mauler moving...it certainly can't keep it's balance, which means it should fall and tumble uncontrolled down the hill. At the very least, prone and flatfooted, no?
Hmmm ... from this excerpt in the IC thread, I suspect that you are right, Marco...
GM StarMaster:
...It's still temporarily stunned, may have taken some damage from its unorthodox mode of travel, but it instinctively flails around trying to regain its feet. There is a large chunk of ground stuck to its nose, perhaps causing it some breathing difficulty and at least partially blocking its vision...
It is not totally explicit, but thing hasn't necessarily gotten up (but is sort of trying) and is stunned. Not sure if it is flat-footed, but mechanically stunned covers that (and more).
From the d20 SRD online:
Flat-Footed
A character who has not yet acted during a combat is flat-footed, not yet reacting normally to the situation. A flat-footed character loses his Dexterity bonus to AC (if any) and cannot make attacks of opportunity.
Prone
The character is on the ground. An attacker who is prone has a -4 penalty on melee attack rolls and cannot use a ranged weapon (except for a crossbow). A defender who is prone gains a +4 bonus to Armor Class against ranged attacks, but takes a -4 penalty to AC against melee attacks.
Standing up is a move-equivalent action that provokes an attack of opportunity.
Stunned
A stunned creature drops everything held, can’t take actions, takes a -2 penalty to AC, and loses his Dexterity bonus to AC (if any).
Of course, only the GM actually knows and can truly rule on that...