There’s a Mini Mushroom in the ? Block at Point 1. If you want to collect all of the Moon Coins during a single visit, make sure you grab it.
The first Moon Coin is located above the platforms at Point 2. It doesn’t remain on the screen for long, so move quickly if you hope to collect it.
When you pass through the Red Ring at Point 3, the red coins appear along the platforms to the right.
The second Moon Coin is located in a hidden room. As Mini Mario, enter the small pipe at Point 4.
The Moon Coin is floating in the middle of the hidden room. Make sure you grab it before you leave the area.
The third Moon Coin is at Point 5, floating on the water’s surface. Dodge the Porcupuffer each time it attacks, and grab the Moon Coin as the platforms drop within range.