There are a few ways to get this star, with the main way being to find the secret slide not too far from the top of the mountain. To point out the general location of the star, it’s found in a little notch right above where you begin the course every time you enter. The entrance to the secret slide is located right by the Fwoosh enemy, which you will come across as you journey to the top of the mountain. There will be a trail of five coins following the Fwoosh, with the entrance being the one flat portion of the mountain wall here; you can see it ripple when you get close, similar to a painting.
The slide here is not really any different than previous ones in the game, although it is definitely the longest one. Note that if you fall off the slide, you will lose a life, but entering the painting will put you right back into the slide portion. After the third Blue Coin, there will be a point where you have to veer to the right, onto a wooden section. If you don’t the straight path will drop you straight into the abyss. Note that you will want enough speed towards the end to make it over the final jump. Drop in the hole at the bottom of the slide to be deposited right next to the star.
The little area with the star is located on the side of the mountain right by where the Chuckya is located. One little trick you can do is pause the game to get a zoomed out look of the map, where you might see this location. It is possible to jump down to it, but you will need to do a jump kick in the air while holding the left stick towards the area. Another method of getting this star is using the float you receive from jumping on the Fly Guy by the giant log. That should give you more than enough time to fly over to it.