New Super Luigi U: Meringue Clouds-5 -- Flame Chomp Ferris Wheel

This level involves dodging Fire Chomps by jumping from Ferris Wheel to Ferris Wheel. These Fire Chomps use up their entire tail to create a giant fireball, then will chase you until they explode. The first Star Coin is at the bottom part of a Ferris Wheel. Go past the giant Piranha Plant and the Luigi-shaped clouds and you'll see the second Star Coin as part of a Ferris Wheel with Piranha Plants. Kill them off, then get the Star Coin. Get the Red Coins if you like and keep going. The third Star Coin is in the air, near the flagpole.

New Super Mario Bros. U: Peach's Castle-3 -- Rising Tides of Lava

Lava fills yet another level. The lava rises and falls, which affects the giant Buzzy Beetles. They hide in their shells when the lava reaches their feet and they will float in the lava, making convenient platforms. There is a subtle difference in the color of the land depending on whether the lava reaches it. There are several mushroom platforms with screws that change their height. The first Star Coin is under a ledge with three giant Buzzy Beetles. When the lava is low, wall jump to get it. The next mushroom with a screw will lower so you can continue. There will be a random item block, and farther along, a set of four brick blocks with a Koopa. The second block of the set has a P-Switch, which makes Silver Coins. The path will split ahead. Take the lower path, waiting for the lava to drop, then quickly running and jumping to reach the second Star Coin, which is under the midpoint. Jump over inclines instead of running up them to make it. Ahead are sets of mushrooms that will alternate in their height when the screw is activated. Between two of the mushrooms are a set of two blocks with a gap in the middle. The gap has an invisible block with a vine to the third Star Coin and a Fire Chomp. Go past the Buzzy Beetles in the pit, past another set of mushrooms, and you'll reach the red pipe at the end. There's a Buzzy Beetle below it so you can reach the pipe when the lava rises. This will take you to the flagpole. This opens the path to the Castle.

New Super Mario Bros. 2: 6-B

This level requires five Star Coins to unlock. You'll see yellow platforms at the start. Jump on them to make arrows appear. The platforms will move in this direction until you hit them again or they run into something, and the arrows will change directions. The third one you encounter will move diagonally. Take this platform to the lower right for the first Star Coin, getting off when it gets near a rock. There are Fire Chomps in this level, so be careful. Stay low and you'll approach a green pipe. From here, you can reach the other floating rocks. Nearby and above is a set of two item blocks. Jump on them and hit the invisible block over the item block to the right. It will make a vine appear. It will take you to another platform. You'll find the second Star Coin here between two walls. You'll drop to the midpoint. In this part of the level, there are Bullet Bills and Banzai Bills. There are also Gold Rings for a lot of coin potential. Take the platform to the upper right, past the Red Coins. Near the highest Banzai Blaster is the third Star Coin. To the right is the flagpole.

Coin Total: 46,694
I completed this level after beating the final boss.

New Super Mario Bros.: 7-1

World 7 is a cloud world. In this level, we'll find platforms on paths. Take the first platform to the right, then transfer to the higher platform. The platform will fall off its track and drop to the lower one so you can get the 1st Star Coin. It will go to the end of the line at the left and go back right, then fall into the void. Jump to the clouds to before it falls off. Here, you'll need to move quickly to get on the flying item block. Get on it before you reach the winding path of the platforms and don't hit it. It will take you over the void to a pipe. The pipe takes you to an area where you'll find lots of coins and ropes on gears. The ropes on gears will take you to the 2nd Star Coin and a green pipe back to the main level. There are more platforms on paths, but this time you'll have to contend with a respawning Fire Chomp. Fire Chomps have a tail of fire which represents how many flames they can shoot at you. If you don't stomp it before the tail runs out, it will explode. There are Red Coins in the area. Transfer to another platform which takes you to the pipe to the flag. To reach the 3rd Star Coin, take the platforms instead of taking a ride on the flying item block. Go up the pipe at the end of the path, then take the higher path to the 3rd Star Coin.