Pause game play, and, after that, press Up, Down, Left(2).
Defeating the Joker
When you reach the Joker, equip the Defensive Suit. After that, constantly ram him with the Shield Punch. He should go down after about fifteen hits or less.
Level 2: Skip robot Boss
Play level two (Wayne Enterprises) and after about two to three elevators, defeat all the enemies to get the key. Then, walk past the elevator. You should find two more easy enemies guarding two metal creates. Defeat the enemies, break the crates (you must have the Offensive Suit) and go through the door. You will find a room with a bull enemy in it. If you have the Nimble Suit with you, Double-Jump onto the cabinet in the room and collect either an extra life or a full health bonus. After you defeat the bull, go to the elevator and you will arrive in the room after the robot Boss.
Level 3: Block toxic breath
You eventually encounter snake enemies with toxic breath that does severe damage to your health. However, if you have the Defensive Suit the breath will stop at the bat-shaped shields and will not affect your health.