Thanks to Smaz for providing this guide and the descriptions and images that follow.
Doll #1
Inside the mountain you will find a room in which has several axes swinging side-to-side and log platforms which need to be slowed down in order to traverse. On the floor, below, will be a Grimly doll, hidden behind some of the upper platform support beams.
Doll #2
You'll come across a room with many platforms which need to be slowed down, via a Grimly, in order to cross. This room contains several tombstones in one area, before needing to slow down time and cross some swivelling platforms to the left. Smash the tomestones up and follow the path around in order to find a voodoo doll hidden behind the final tombestone.
Doll #3
The misty room holds host to a Grimly Doll. After the first thin path, the ground will open up into a more spaceous area. Head to the right and listen out for the voodoo doll noise. Head towards the screen, once slightly right, to find the floor continues downwards, revealing a secret area, in the mist, where a Grimly doll sits.
Doll #4
In the room after the misty area, you will find a weighted platform away from the screen. The best way to go about obtaining the voodoo doll is by using a Grimly and following the path as quickly as possible, or by jumping from one side to another, in order to stop the platform from tipping too far to one side and dropping Crash into the abyss. A second, co-op player, would be useful for this doll, so that you can distribute the weight of the platform between the two of you, to keep it still enough to reach the doll.
Doll #5
After Uka's mission, you will head out into the open, via a Yuktopus. Once outside, you will spot the a Grimly doll on a ledge to the right. You can either double-jump up there or reach it via a digging spot to the on the floor.