Enter these on the password screen:
To get unlimited lives it's kind of tricky it usualy work better with 2 players but it still possible with 1 player. First get to a boss and make sure you have an extra hero to help you (Captain America, Dare Devil, Ghost Rider ect.) Get the boss to low health and get yourself to 1 life and low health. As soon as he kills you press "L" to get a heor's help he will kill the boos. In the next level you will have zero lives and you can die as many times as you want. BUT MAKE SURE IF YOU HAVE ZERO LIVES DO NOT PICK UP LIVES IT WILL SET IT TO 1 LIFE AND YOU HAVE TO RE DO IT. If you have zero you can die and it will go to 9. I honestly dont no how many lives you truly have but it is alot probably like 100 but that should be more then enough.