World 1-1: Super Bell Hill
Stick to the lower path in the level's beginning to reach this clear pipe. Press upward as you move travel through it to pop out of the top and grab the game's first star.
After the big drop from the clear pipe, you'll spot a rabbit by the checkpoint. Catch him to earn another star.
Stamp: Cat Suit Mario
In the same area is a green warp pipe. Hop inside to find a small room with a clear pipe. Ride it around the loop to grab this.
Head back through the warp pipe and use the Cat Suit to climb to the top of the cliff the warp pipe goes into. Catch the giant rabbit up here to earn a Mega Mushroom, then run across the bridge in your mega form. On the other side, ground pound into the bricks to drop to a lower area, then keep charging forward to break through one more set of bricks to reach the course's last star.
World 1-2: Koopa Troopa Cave
You can't miss this one - it's floating among the cloud platforms early in the level.
Enter the warp box just past the checkpoint. Inside, you'll have 10 seconds to take out some Koopa Troopas. Do so to earn another star.
Stamp: Gold Coin
In the very next room, jump near the wall to find some invisible blocks. Do this to reach the ledge above, then enter the clear pipe. You'll wind up in a small hidden room with lots of coins and a stamp.
Head back through the clear pipe, then jump across the platforms to your right. The next star is inside a tower of Goombas. Bounce or ground pound your way through them to grab it.
World 1-A: Chargin' Chuck Brigade
Simply take out the Chargin' Chucks to earn this.
World 1-3: Mount Beanpole
At the very start of the level, climb the tree to your left to find this.
As you climb the mountain, you'll see POW Blocks. Hit the third one to break down the wall of bricks behind it. Enter the warp pipe it reveals, then hop on the blue switch inside the cave. Collect all the blue coins before time runs out, and another star will appear.
Stamp: Cat Suit Goomba
Just beyond the warp pipe is a stamp floating high in the air. Use wall kicks to reach it.
You'll need a Cat Suit for this one. Climb the tall tree just before the walkway with the Piranha Plants to find a gear with a paw icon. Swipe it a few times to create a tower, then climb up to find a special cloud that rockets you to a bonus area. Run through this little course to find a star at the end.
World 1-4: Plessie's Plunging Falls
Hit the first ramp with a good amount of speed to reach this.
As you near the end of the level, you might spot a suspicious looking waterfall on the left. Swim right through to find another star inside the small hidden area.
At the same waterfall, bear right (you'll have to replay the level). Hop over the small barrier to grab the stamp along the path.
You'll find this over the last big ramp in the level. Hit it with good speed and take a leap to grab it out of the air.
World 1-5: Switch Scramble Circus
Before entering the warp block early in the level, use wall jumps to ascend to the platform above. You'll find a star up here.
Just after the checkpoint, keep left while ascending the platforms. Hit the mystery box to reach a secret room. You'll have 10 seconds to destroy all the boxes. Pull it off, and you'll get a star.
Just beyond the last star is another series of question mark pads. Time your dash across the moving pads when they line up with the floating star to grab it.
Stamp: Super Bell
When you reach the level exit, hit the question mark pads to lower the tall platform. Wall jump off the curtain to reach the stamp above.
World 1-Special: Captain Toad Goes Forth
The first star is simply underneath the moving platform.
Head up the hill and use the moving platform to reach this.
Head up the next hill and move through the left tunnel to find this.
When you reach the high platform, carefully step between enemies to grab this.
Cross the plank to grab the final star.
World 1-Castle: Bowser's Highway Showdown
At the start of the level is a hollow green star. Hit it to make eight green coins appear. Collect all eight before time runs out to earn a star.
After the moving yellow platforms, scramble up to the gear marked with a cat paw. Swipe it a few times using a Cat Suit to temporarily raise the platforms nearby. Quickly scramble up these and head right to find a star.
Using a Cat Suit, swat a Bowser bomb into the big bricks underneath the cat paw gear. You'll find a stamp behind them.
A little further ahead, you'll encounter a stack of Goombas with a star on top. Get their attention, then retreat to the earlier platforms. Use them to leap to the top of the Goomba stack and grab the star.