Acquire a Beam Box at the beginning of the level and try not to lose it. Ride the platform through the top layer, defeating Boos by shining light on them. If you have Luigi, jump the Luigi Character Switch to release the Stamp then continue to the Big Boo. Defeat it for a bunch of coins then drop down. The path on the left side comes towards the screen and has Green Star #1 on it.
Take the next moving platform and defeat the Peepas. Use the Red POW Blocks to take out the Parabones that follow and if you’re bold, hit the Red Ring and collect all the coins for a Super Leaf which surely helps in this crazy level. Exit via the door at the end to reach the Goal Pole and some more Beam Boxes . Proceed to another movable platform and be ready to jump off to the right side where a Mystery Box can be found. Shine your light on the six Boos to defeat them and reveal Green Star #2 .
You end up on the far side of the gap with a bunch of doors. Take the right one to reach the second floor then take the right one again to reach the home stretch. This next platform spins and is pretty narrow so clear out the Peepas as best you can making it past the Parabones and Big Boo at the far side. If you can defeat Big Boo then claim Green Star #3 without trouble, otherwise lure him out and quickly grab it to avoid damage.
Exit through the door at the end then leap from above to the Goal Pole.