This can only be done in either Survivor mode or MultiPlayer on the Survivor level:
Top of Level / Invisible Walls: When you start off, take an immediate right. Let the pad launch you to the top ledge thingy, and don't move while it launches you. Get on the flat part of the bow lookin thing and turn into a morph ball. Set all three of your bombs while staying perfectly still. Right when they start to go off, unmorph, and you will go flying REALLY high. At the very peak of your launch, jump and push the D-Pad towards the ledge. You will be able to walk up a steep slope, and fall down a big, roofless hole in the ceiling. Now you are back in the level, except you can only see the monsters and the walls of the side you came from. It's helpful to use the radar to walk around in here.
Side Wall:Go the same way as you did the first time, except when you are on the caged floor, do not step on the pad. Keep going and hop onto the very thin ledge running alongside the wall. Morph into the ball. Use the previous technique to get onto the top of the wall from there. Run on top of that towards the slanted hill. Jump to try and land on it, but you'll realize that there is nothing solid there, it is where the program stops telling the game to put walls. Instead you'll land on a flat beam. You can run out to the edge of this, and just missile, beam, and lob the heck out of your enemies down on the lower or parallel floor. If they eventually find out where you are, it will not matter, as they can't harm you, you can only get them.
Top of the Towers: Follow the direction in the first glitch, and step on the pad. Jump off of the block, and run onto one of the perpendicular sides of the level, one that has those big towers. Use the morph bomb trick to make your way nearly to the top. You can eventually get on the top of one of those slanted beams, and get a bird's eye view of all of your foes sitting there, wondering who the heck is shooting them.
Remember not to abuse these too much, because a good gamer does not camp the whole match using these glitches. Particularly the second one is really cheap, because you cannot die at all. So be a good gamer and get out there in the middle of the fight and don't be scared to die a few times. Good Luck!