It's snowing in this level. There are green switches with platforms that flip out. This is how we get from yellow checkered platform to yellow checkered platform. The second green bridge requires either a long jump or a slow descent. One of the middle item blocks on the large checkered platform high up has a Poison Mushroom. Here you want to trip all three green switches, as the first Star Coin is over the left bridge. Be quick: these bridges won't last long. Next, we warp using an orange Mystery Box to the midpoint. We activate both bridges and reach the first orange Mystery Box, which warps us back to the midpoint for a clock high in the sky. The second orange Mystery Box warps us to the second Star Coin. The third warps us to a large checkered platform with three green switches. They form a staircase over the switches and will block you in unless you move away from them quickly. The farther switch takes you to the flagpole, where I got a 1-up.
Take 2- I fell.
Take 3- I fell.
Take 4- The third switch can be found by using the bridge at the top of the green staircase. Jump from the second turn and slowly descend to a small platform with the third Star Coin. We got a 1-up at the flagpole.