I suggest you try some of the wierd vehicle glitches like on the bridge in Metropolis instead of driving the tank take the warthog (2 player only) and waste your marines, all of them. Then hit the 2nd wraith with it and it should send the wraith flying, roll it over or totally destroy it for some reason but it all depends on timing and positioning and there must be 2 or more ghosts left running and piloted or the ghost in the tree for this you need to be on the level where you are the arbiter and are on the level with the waterfalls and ghosts. First in the area where the brutes on ghosts jackals the only exit has a rock in the middle and a backwards ramp on the right side stopping you from going that way, then kill all the ghosts, jackals and brutes except for one ghost and driver now you must board it an drive it between the 2 raised grassy tree covered "Islands" and stop moving the brute should board you so let him the ghost will shoot into the air killing the brute and parking it ontop of a tree if done right. Try this every once in a while sometimes it just wont work for some reason same goes for the warthog-wraith glitch.