Can be found in world 3 Holiday Canyon:
1. Enter Holiday Canyon
2. Head forward over the bone bridge
3. Head left once you can till you just pass the entrance for level Present Danger
4. Jump onto the wooden patio and you'll find the rock golem in his little cart shop (press x).
5. I purchased a hat and outfit and the achievement popped up.
*Also can be found in world 4 Spookington (on the right of the entrance for first level Carnival Court)
*This achievement has since moved from Guardian Trials DLC to title update so it is available to all