World 8-Airship

Coin 1 (before checkpoint)

When you reach the first cannonball barrage, use them to bounce up to the Star Coin.

Coin 2 (after checkpoint)

Use the platform just after the checkpoint to reach the second Star Coin. It's easiest if you move it a little ways past it first, on the right, this way the two enemies within are lured against the wall, giving you space to jump in and grab it on the left as the platform passes by underneath.

Coin 3 (after checkpoint)

Drill this last screw to reveal the final Star Coin that lowers from the platform ahead. If you're playing single-player, you need a Propeller Suit to reach it--just jump to it then propeller out to the right. However, if you're playing multiplayer, simply have someone jump at it, then bubble-up immediately afterward to avoid certain death.