Infinite 1-Ups
On World 1-2, having passed the checkpoint flag, you will see a trio of koopa troopas and another three coin rows.
If you stand on the first row of coins that is on the floor, and walk onto the koopa below as it comes beneath the coin block. You should be able to bounce up and down off the koopa to get infinite 1-ups in this fashion - at least with practice.
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