World 9-6: Honeycomb Starway
Early in the level, you can spot an exclamation mark block in the air - the best way to hit it is with a throw from the Boomerang Suit. Do this to generate a path to the right, letting you reach the star.
Just after the clear pipe is an open section with tons of Para-Biddybuds. Take them all out - again, the Boomerang Suit is preferred - to spawn a star.
When the ice and lava panels start slamming into place, the third star will be above the lava. Use - you guessed it - the Boomerang Suit to safely grab it.
Just beyond, there will be a large group of bee enemies. To the right, floating in space, is the stamp. That's right, ladies and gentlemen, it's Boomerang Suit time once again.
World 9-7: Gargantuan Grotto
Stamp: Mega Mushroom
You'll grab the Mega Mushroom early in the level. Run to the right, but don't stomp through the big blocks on the ground yet. Instead, jump into the cluster of blocks above the grab this.
Just beyond is a wall of those mean purple blocks. Tap them on the GamePad to make them disappear for a second, then step into the alcove. Wall jump up to grab the star in here.
When you see this big blocks underwater, surface. Hit the question mark block here to find another Mega Mushroom. Jump back into the water and head right. Leap upwards from the bouncy mushrooms to break through several layers of big blocks - there's a star up here.
Instead of taking the warp pipe out of the water, swim directly up. In this hidden alcove is another warp pipe. Take it to reach an area with a switch and a question mark block. Hit the block first to grab another Mega Mushroom, then step onto the switch. As Mega Mario, collect all the columns of blue coins the switch generates to spawn a star.
World 9-8: Peepa's Fog Bog
Captain Toad is being harassed by ghosts at the northern end of the starting zone. Look east for a glowing spot in front of a tombstone, then ground pound it to reveal an Invincibility Star. Grab it and use your powers to take out those ghosts, freeing Captain Toad and earning you a star.
Just past the checkpoint are two Snow Pokeys and two mystery boxes. Enter the one on the right to reach a hidden area. You have ten seconds to collect the star here, but it will disappear when approached. Grab a snowball, back up, then chuck it at the star when it reappears. Star collected!
Now take out one of the Snow Pokeys and grab yourself a snowball. Take it down the left side of the next walkway, then chuck it at the elevated star to collect it.
Stamp: Cat Suit Rosalina
Before taking the warp box to the level's end, make a right along the walkway. Leap the gap to find a stamp over here.
World 9-9: Cosmic Cannon Cluster
Stamp: Cannon Block
Grab the Cannon Block from the first platform, then continue on the switchboard. When you see this group of question mark blocks, hit them with a cannonball. This will generate a path of bricks to the stamp.
After ascending the wall with the cannon trio, move to the right ledge. Use your Cannon Block to blow through the cracked wall to the star on the other side.
While in the underwater section, look for this group of bricks. Bust through to find a star inside a hidden area.
While on the second switchboard, you'll pass some exclamation mark blocks. Shoot the second one to aim your track towards the star. Shoot it with a cannon ball to collect it.
World 9-Special: Captain Toad Goes for a Spin
Press the switch to rotate the cube, then drop down a level. When the enemy is neutral (purple) move past him to grab the first star.
Drop to the ground and hit the switch to rotate the cube again. Drop to the new ground level, and head up the ramp to the second star.
Hit the switch on this same ramp to rotate the cube, then drop to ground. Move to the corner to spot the third star behind some enemies. Grab it while they're purple.
Move to the switch up the ramp, but don't press it yet. Press it when the nearby enemy is neutral, and the cube will rotate, dropping you onto the enemy's head. Now you can safely grab the star.
Hit the switch to rotate the cube one last time. Carefully drop down the ledges, watching the enemies for neutrality, to grab the final star.