The first Moon Coin is located in a small nook at Point 1. If you have a Super Leaf, use Raccoon Mario’s tail whip to clear the Fishbones out of the area. If you no longer have this power-up, approach the Moon Coin from below and dodge the enemies patrolling the area.
The second Moon Coin is located in a hidden area. To find it, enter the pipe at Point 2.
After you pass through the pipe, grab the Moon Coin to the right.
Pass through the Red Ring at Point 3 to reveal the red coins to the right. To collect them, zigzag along with the water currents and avoid the patrolling Fishbones.
As you approach Point 4, draw the Fishbones away from the Moon Coin. Slip between the enemies—or use a power-up to defeat them—then swim over and grab the Moon Coin.