Gordon goes and climbs out of the river, ahead of the torrent. Okay, so it can't see well but if it finds him it can easily crush him. With tentacleslike legs, tripping it is not going to be an opinion, but those trees growing on it may prove useful.
Okay, do you have anything that might be able to harm the troll? Yes, the lava gun should be able to hurt it, but it only has one shot. Now, he doesn't know where the organs are in this thing, but likely the head has something important to it. So Gordon takes his grapple gun out, and quietly checks to make sure its working right.