There are many special achievements in "Sonic Mo Chao's skill shop (to the left of Qingshan) buys all the skills he has to offer.
How to make the crazy Skilts achievement in Sonic Chat Generations reboot
Crazy Skilts
Acquire all skills.
As the achievement icon suggests, you need to go to Omochao's skill shop (to the left of Qingshan) to purchase all the skills he has to offer. Some skills are unlocked in the store after completing certain challenge behaviors, and some skills are obtained in your skill inventory immediately after completing all 5 red star rings in one behavior.