First do the debug mode. Then choose enemy option. Choose any enemy (a level 2 ninja would be thebest). Then choose Pad-2. Then run away from P2. When you see a question mark (near your life bar)run back to P2. Now Player 2 can move the enemy you have selected for him/her. Try level 4 (The checkpoint) at the bridge so you and P2 can fight and knock each other off.
Note:If leave Player 2 he/she will dissapper.
Note:If P2 fall in deep water he/she will drown
