World 4-3

Coin 1 (before checkpoint)

Bounce off the enemy onto the block to reach this coin.

Coin 2 (before checkpoint)

There are a couple of ways to grab this coin unharmed. Either use the penguin suit (combined with the star) to slide along the water and leap into it, or use the tiny-mushroom from the box above to jump into it.

Coin 3 (after checkpoint)

Just after the checkpoint, you'll find a tiny horizontal warp pipe just past a couple of vertical ones. If you're not already tiny, you can find a tiny shroom in one of the boxes just above where the second coin was. After warping, you'll find your coin.