You can make Batman invincible with the following steps at the title screen (the one with the Batlogo): press up 8 times, down 12 times, left 15 times, right 19 times and option 1 27 times, press A or B to start the game. Once the action starts, press pause. Then use option 1 to skip to the next level, option 2 to make Batman invincible! Falling can still kill you, however.
From Video Games and Computer Entertainment.
Check in the gift after all the bad guys come out.