The Porcupuffer on World 6-5 is extremely irritating! It will leap out of the water and attempt to gobble you up. Either learn to time its attacks so you can dodge them, or use the Fire Flower power-up to dispatch them quickly. Even if you get rid of Porcupuffer, though, another will always eventually take its place.
Grab the Propeller Block at Point 4 and use it to float across the level and grab the coins as you go.
