1. In the room where the painting for Jolly Roger Bay is, jump to a high
ledge on the right side (facing the painting). You'll enter an underwater
area; swim around and collect the 8 red coins for this star.
2. In the character switch room, jump into the southeast stain glass window
of Peach to reach the Princess's Secret Slide. Simply slide down to the
bottom and hit the yellow box for a Power Star.
3. Replay the Princess's Secret Slide and get a faster time than 21 seconds
to get a second star.
4. In the Goomboss Battle area, collect the 8 Red Coins to win a Star (see
that section in the walkthrough for the locations of these coins).
5. In the Goomboss Battle stage, after you go down the slide, head to the
right. You'll find a hill you can go up, then on the long platform, a star
switch. Step on it to make a star appear atop a cage. Run to where it's
located on the map, then wall jump (yes, you need Mario for this one) to
the top. Once there, walk over to the Power Star to get it.
6. In the Wing Cap stage, simply collect all 8 Red Coins (pretty easy to do,
look in the walkthrough).
7. In Bowser in the Dark World, when you get to the end by the pipe, you'll
spot a star switch. Hit it to make a star appear on a platform above the
tilting platforms before the hill. Go back down and tilt on one end of the
platform to make the other side rise, then quickly jump up from it to the
higher ledge (if you have Yoshi, just flutter jump from the base of the
hill to the first platform, then flutter jump from there). Either way, the
star is on the last ledge for you to get.
8. In the Bowser in the Dark World area, collect all 8 Red Coins for a star.
9. In the Rec Room, jump into the painting of the Sunshine Isles. There,
collect the 5 silver stars to get another secret Power Star.
10. In the courtyard where you enter Big Boo's Haunt, you'll find several
smaller Boos. Defeat each of them to get a red coin; collect all 8 for a
star.
11. In the castle's courtyard, break the blocks to the right and drop into
the hole to reach the Battle Fort. Collect the 5 silver stars there to
get a secret star.
12. In the Big Boo Battle, collect the 8 Red Coins to get a Power Star (the
locations are in the walkthrough for that area).
13. Go to the Big Boo Battle as Luigi. In the third room, hit the red box and
make him invisible. Now, quickly jump/flutter through the next room to
reach the final chamber. Run across the bridge and jump into the ghost
painting to run into a hidden star!
14. In the Hazy Maze Cave as Mario, get to the underground lake. Ride the
Nessie to the door on the ledge you can't reach by swimming. In there,
drop into the portal to reach the area Behind the Waterfall. Jump across
the ledges to the last one (it's the one with 2 red coins on it). Use the
flower from the red box to invoke Mario's floating ability. Then, simply
fly straight up to this hidden star.
15. In the Behind the Waterfall area again (see the previous listing here for
details), collect the 8 red coins (use Wario and hit the red box to get
his metal power) to get this star.
16. In the room where the portal to Hazy Maze Cave is located, there is a
Toad. Talk to him to receive a Power Star.
17. In the Bowser in the Fire Sea stage, collect the 8 Red Coins to get a
Power Star (check the walkthrough for details on that).
18. In Bowser in the Fire Sea, you must find a star switch. I highly
recommend you use Luigi for this one. It's on a high ledge above the
sinking/rising poles in the end area. Hit it, then jump to the other high
ledge up here. Backflip and copter across the lava area below, and break
the glass ball to obtain your Power Star!