In Siege mode in multiplayer, select either the Korriban or Desert Rescue map. At the end of each map, there is an arena with a rancor. When you go up to it, he'll most likely pick up and eat you, killing you right away. However, there is a way to survive this.

In order for it to work, you must be a Jedi with Force Protect, which is only on the Rebel side. Go up to the Rancor and let it pick you up. It will hold you there for a couple seconds. When it starts to bring you to its mouth, turn on Force Protect. You will be eaten but still alive.

Now that you're trapped in its body, you can only see the rancor, not yourself. You cannot move around, but you can use your lightsaber. While you're in there, you are protected from enemies, except for missles due to splash damage. You can swing your lightsaber around which hurts the rancor.

When it dies, you will be free again, but you'll notice you can't see your character! Nobody else can either. You, your saber, your force powers, all completely invisible. If someone happens to target you, your name and stuff will appear but
it'll look like nobody's there. If you die, you'll respawn back to normal.