Leave Level Boundary In Gemini:

Go to the beam rifle in the back with a partner and swords. Go through the Blue teleporter and you will be outside. Turn to your left and walk on the small pole that is sticking out of the edge. Jump to the small slanted box and crouch. You will slide for a moment, then land on a flat surface. Have your partner do the same thing. Walk up it and sword cancel up to the roof (press R + X at the same time). Go to the edge and have your partner jump toward you and sword cancel. Go to the next wall and sword cancel over it. You are now past the map's boundaries. Walk straight to the end and hit the invisible wall. Then, walk left and fall. Lean against the invisible floor while doing so. If done correctly, you and your partner will be at the very bottom of the level.