First, go to the Pass of Caradhras on the map, not the level, though. Go down the steps and do the boat thing to get the mithril brick. WHILE one player is doing this, player two holds open their character inventory. There should be a boat there. DON'T click on it until player one is done with the boat thing. Click on it, then you can ride around in water, cross rivers, and only projectiles can harm you! WARNING: IF YOU GO INTO THE LAKE AT PASS OF CARADHRAS, YOU CANNOT GET BACK OUT.