Superola Champion Edition

On my first play through this failed to unlock for me on my 100% save file. I can't be sure but I believe buying the costumes too quickly may have been the problem.

So to unlock I played through on a new file until I had access to the final costume shop.

Then I replayed level 1-1 until I had 300 coins which is the total needed for all the costumes.

Next I force quit the game so if it did not unlock, I could delete the local save while the game was running then load the game again to use the cloud backed up save.

Then after purchasing each costume, I would back out of the store. Wait a few seconds until the saving prompt has finished. Then go back in and purchase the next costume, back out and repeat until all costumes were purchased.

Doing this the achievement unlocked for me.