(OOC: Oh duh, when you said 'grabs' I assumed Grapple, but you added his Trip bonus and not his Grapple bonus, so you must have meant Trip. Good. It's Grapple modifier is 5 higher than its Trip modifier. Thus, you successfully trip it, even with the 13, since it rolled quite low)
*Valan somehow manages to knock the corpse monster onto the ground, prone and much more vulnerable to attack. However, his follow-up attack is doomed to complete impotence.*
(OOC: Hasin?)