You'll encounter a hollow green star early on; hit it to spawn eight green coins. Collect them before time runs out to earn a star.
Take the upper ledges inside the tunnel. Leap above where the warp pipe is to find a cloud platform. Leap to the next alcove to find a star.
Now enter said warp pipe. Inside, you have to touch all the tiles before the music stops. Do this to earn a star.
This is hidden behind a treetop at the start of the mountain.
About halfway up the mountain is this group of bricks. Bust them up to find a warp pipe beyond; take it to a secret area. Hit the blue switch here to spawn three sets of blue coins. Collect them all before time runs out to earn a star.
There are three trees at the top of the mountain. Leap from the rightmost one to reach the star high in the air.
Use a Cat Suit to climb the first red gate. The star is on the upper path here.
Just before the dip in the stream, you'll see this floating above the water. Move towards it to see some cloud platforms become visible. Use these to reach the star.
Don't take the warp box out of the level. Instead, use your Cat Suit to scramble up the wall at the edge of the course. There's a star up there.
This appears above you when you go through the red door. Hop up the platforms to grab the Boomerang Flower, then toss a boomerang to grab the star.
The second star is on a ledge just below where the Boomerang Flower was.
This is on a high ledge just past the stack of Goombas. Wall kick up there, or scramble up with a Cat Suit to grab it.
You'll spot this inside a large clear pipe. Throw a baseball into the pipe to clear the spike, then hop in to claim your prize.
When you reach the rooftop, you'll see a hollow green star. Grab a Propeller Box and hit it spawn eight green coins. Collect them all before time runs out (you need the Propeller Box for the ones over the edge) to spawn a star.
As you ascend to the top, tap the Bowser gong on the GamePad; this spawns a warp box. Use it to reach a little room with coins and the level's last star.
This hollow green star is right at the start of the level. Hit it to spawn eight green coins; collect them before time runs out to earn a star.
When you reach the third warp box, don't hop in immediately. Instead, look to the side of the platform for a narrow planked walkway. Follow this to find another star.
After the third warp box, grab the Mega Mushroom from the nearby question mark block. Cross the planks as Mega Mario, continue past the path to the next ship. Leap up from this dead end to grab a high altitude star.
A Tanooki Suit is key for every star in this course. This floats above the lava near a set of Parabones. Leap to it when the platform beneath temporarily rises.
This one's tough to get. It's on top of the second group of rotating spikes along the zigzagging path.
The last star is on a cloud platform behind the warp pipe at the level's end. Use a Tanooki Suit to leap to it.
This bonus stage is just series of battles, all of which have ten second timer; complete the battle in time to receive a star. The first is against a trio of Chargin' Chucks.
The second is against three Snow Pokeys.
The third is against a pair of Hop-Chops.
The fourth is against a trio of Boomerang Bros.
The fifth is against a Coin Purse. He's hiding by the upper left trio of grass tufts.
The sixth is against three stacks of Goombas.
The seventh is against a trio of Fizzlits.
The eighth is against a trio of Magickoopa.
The ninth is against a trio of Piranha Creepers.
The final battle is against a trio of Hammer Bros.