kewl, I found a super easy way to get into MB tunnels. Just put your back to the tunnel and shoot a charged missile at the ground a little bit in front of you. The blast will push you right through the barrier. I'm pretty sure this works in multiplayer, and if it does, it would be fun to confuse your opponent by walking around in a MB tunnel! :P
Edit: I just remembered something. It helps to walk backwards against the wall while you shoot the missile. Some barriers don't let you through if you don't.
Edit: I just remembered something. It helps to walk backwards against the wall while you shoot the missile. Some barriers don't let you through if you don't.