this is more a trick then a cheat, but in level 2-4, at the very end of a level, there is a turtle walking down the stairs leading to the flag. at about the 4th step, jump on him. here is where it gets hard. you need to jump on him so when he ricochets off the wall, you continue to jump on him. after that, don't ove so mario is just jumping n the turtle, and after a while, he will get 1-ups, and as long as you don't move, your lives will continue to go up till 99.