Chapter 6-1: Mustacho's Dungeon
Amulet Piece #15:
When you reach the room with the three doors on each side, go to the top right door and draw a vine so that you can push and hit it with the fire power. Cut it and drag it inside the corridor and blow open the square door. Drop down the green narrow passage and you will then need to attach a vine to a branch after hitting it with the fire power, then blow open another door on the lower right. Make your way down through that door to find the piece.
Chapter 6-2: Breakout
Amulet Piece #16: When you roll Felix into the room with the two bombers on each side of the upper level, take them out using the fire power and then destroy the shining wall to the left. Ride the pillar up on a branch and then hop off and enter the opening to find the piece in there.
Chapter 6-3: Death by Lava
Amulet Piece #17: Near the end of the level, you will need to use a water spout to go up and around a few platforms of spinning blades. When you reach the top, instead of going right, keep going up and there will be a rope there you can grab. Climb up it and jump over to the platform to grab the piece.