After playing for a long time, I found the best place to get power-ups.
All you need to unlock this place is a "feather".
-Once you get the feather, go to "DONUT GHOST HOUSE", & go inside.
-once iside, you will see A CRAP LOAD of ghosts swarming everywhere.
Go to the right until you reach a hole in the gound.
-While wearing your cape, run to the left & fly up towords the ceiling
(while trying to avoid the ghosts).
Fly through the opening on the far left of the room & then go right again.
-Walk all the way to the right & drop down (still trying to avoid the ghosts).
At the bottom, there are either 3 or 4 blocks with 1ups inside.
Then go through the door.
-Once through the door, go through exit & you unlocked it.
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The TOP SECRET AREA is made up of 5 blocks...
The 2 on the left are mushroom/fire flower blocks
(you'll get the fire flower if you've eaten a mushroom already)
The 2 on the right are mushroom/feather blocks
(you'll get the feather if you've eaten a mushroom already)
And the block in the middle is a Yoshi block.
(And you've unlocked the different colored Yoshis, you can choose them depending on what
your current power-up is.
-NO POWER-UPS = GREEN YOSHI
-MUSHROOM = YELLOW YOSHI
-FIRE FLOWER = RED YOSHI
-FEATHER = BLUE YOSHI
Hope this helps
-Zath