Instructions
Grab the first star coin early in the level by using a propeller suit power-up or a Lakitu cloud. Find Yoshi in a question block and use him to eat Lakitu. Steal Lakitu's cloud and pilot it to the coin, which is hidden behind a cloud.
Use Yoshi to eat the piranha plant that spits fire, which is located just before the midpoint flag of the level. Spit the fireball from Yoshi's mouth to kill another piranha plant nestled between some blocks just to the left.
Move to where this plant was located and a trail of coins will appear. Follow them to a secret underground area. Grab a light brick to help you see your way to the second star coin.
Steal a Lakitu's cloud to get the third star coin. This coin is located high on the map just past the midpoint flag. Use Yoshi to eat Lakitu and ride the cloud up to the right to get the coin. You should now have all three star coins in World 2-5.