Big Heads:
Get the three hidden stars located in This Ol' House GP in single player mode.They are located behind the jack-in-the-box close to the start; in a bon-bon located on the wooden planks above where is possible to see the man taking a bath down below; and in a pipe that is located directly after the big spider, the star should be to the right once you go through the pipe.
Color Change:
Get the three hidden stars located in Hoedown GP in single player mode. They are located in the first party popper after going up the convey belt; underneath the tapping foot of the woman with hairy legs; and at the end of driving the hay bails road drop down slowly and land on another hay bail, below that has another star on it.
Concept Art:
Get the three hidden stars located in Jungle Jamboree GP in single player mode. They are located behind the first jump; after passing the first check point do a 90 degree left turn and go in the square hole that is covered in fire (a short cut), and after going through the short cut go ahead a bit more; and the last one should be visible behind a broken statue head laying on the ground -- you might need to jump in order to get the star.
Micro Marble:
Get the three hidden stars located in 911: Emergency GP in single player mode. They are located at the first sewerage drain to the right at the start; among the group of boxes close to the start; and behind a wall after going down a flight of stairs.
Micro Soccer:
Get the three hidden stars located in Beachside GP in single player mode. They are located to the left outside of the submarine helmet; behind the sand castle before the beach ball; and underneath the first jump at the very beginning.
Mirror Tracks:
Get the three hidden stars located in Toy Town Sci Fi GP in single player mode. They are located after the first teleport go left, there should be one located on underneath a pipe and next to a cup; after going through the first teleport, another star is located to the right on a arm of a chair; and a star is located behind a pillar to the right of the speed up the has the freeze and pause power-ups.