New Super Mario Bros. 2: 6-4

We get a break from the lava in this level. Go left of where you started for the first Star Coin. More coins will appear when you get it. This level features the platforms carried by ghosts. There are also Boos and crows. There is a rotating item block guarded by a Boo and a crow. Lead the Boo away and jump on the rotating block, then jump up to hit an invisible block. It's a little to the right. It contains a vine that leads to the second Star Coin. The stones you have to jump from are rotating, so be careful. You'll drop down a short distance from the midpoint. Red Coins are nearby. Soon, you'll reach a ring of circling ghosts. In the center of their ring is the third Star Coin, in the gap. Drop down when there's a gap in the ring and wall jump back up. There is a large platform carried by a ghost along a path. Dodge crows and other ghosts, then transfer to one of two platforms. Both will take you to the flagpole.

Coin Total: 46,824
I found the second Star Coin after defeating the final boss.

New Super Mario Bros.: 6-4

This is another rock level. There are firebars located through out the level, especially in areas where you have to sidle on thin ledges. Wall jump past the first firebar for the 1st Star Coin. We then sidle past more firebars, including a large one. Hang from the ledges to avoid taking damage. The ! Switch makes blocks appear so we can wall jump up. You'll reach the midpoint. From there, jump to the left for the 2nd Star Coin. Go to the right and take a pipe to the next area. You'll have to sidle as well as time your jumps to platforms, as you won't be able to jump as high. In this area, take the platforms up to the green pipe and go to the right for the 3rd Star Coin. Take the yellow pipe, then the green to the flagpole.

Super Mario 3D Land: 6-4 -- Step to the Beep Part 2

We hear a familiar whistle when we start this level. Ahead of us are three platforms: blue, yellow, and pink. They appear with the higher-pitched beep and disappear with the lower-pitched one in the above order. We cross them, hop over a walking Thwomp, and hop over some more forming stairs. I died from the spiky enemies.
Take 2- We reach the door, but jump from the top of a walking Thwomp to a ledge with the first Star Coin. We go through the door to find more blocks and walking Thwomps. At the top of the stairs is another door with the second Star Coin above it. Outside is the midpoint. We get a Tanooki Suit from Red Coins. The third Star Coin is above the block with the spike bar. It hit me and I fell off.
Take 3- I fell after getting the third Star Coin.
Take 4- See Take 3.
Take 5- See Take 3.
Take 6- The gold block appeared. We get the third Star Coin and a Tanooki Suit. We then have to dodge swinging spike bars with the platforms as a safety net. We get a 1-up at the flagpole.