Go to the part in the level where you get the key. There will be a shell you have to pull out just outside of the door where you get the key. Pick up the shell. Throw it and jump on it. Let it run you to the very bottom. Jump off the shell at the very last cliff. Go back up one more cliff, where you can pull out the veggie hearts. The Shy Guys will come falling down, because they can fall of the cliff but cannot reach you if you are on another cliff. They will fall down all the way to the shell. The points will keep adding up, until you get an extra life. Just wait until you get 99. The hard part of this trick is to get away from the Shy Guys and the shell. You may lose one life in the process.

Go to World 3-3. Climb the ladder, then jump over the spark enemies to the door over on the ledge. Find the red grass patches; the last one is a shell. Pick it up. Go back to the bottom of the area, and then toss the shell into the doorway. Stand on the ledge and wait. After the shell defeats enough Shy Guys to earn 1,600 points, you will start earning extra lives. You can easily and quickly earn up to 99 lives.

Climb the steps and go out the door. Go out and turn to your right. Keep going to the right until you reach to the first gold type of door. Enter it. Turn to your right and pick up the big POW. Hold [Forward] + to run down the aisle. When you reach the first jumping animals throw while still running. Follow it down (by running with + [Forward]) until it stops bouncing and disappears. You will receive two free lives. Return to the door on the far right. Go through it and you will be outside. Go back in and repeat as many times as needed.

Start the level and go through the door. Next, run past the enemies (the bombs that the birds drop) and enter the door at the far right. After going through the door there should be a plant to your right. The plant is actually a gigantic POW box that bounces four or five times. If you picked up the plant and still are holding the gigantic POW box, hold or [R] (Run) and throw it at the first Spark Ball. After you throw the box, run after it. If done correctly, the box should kill so many enemies that you should get two to five lives. Repeat this trick to get 99 lives.