Get a crossboy and shoot and keep youre distanse and let them blow up!

In the first level in the train when you battle Lazarus (make sure hes about to hit you) jump infront of hit and he will make you fly back real far this could get you out of the barrier.

I did it whit my friend so I know it works.

In the first leve while in multiplayer mode, as soon as your supposed to go to the part when you ride the horses, get killed by either having your partner killing you or getting killed by Lazurus. Then your horse will be running without moving it's legs and you will be flying but wont be able to shoot and once the undead riders or whatever there called kill you you will come back and be on your horse

If you want kill those zombies faster than finding a tumbleweed in a ghost town.Just shoot their heads.