Okay, so once you own 10, Skeletal Marionette Parts can no longer be obtained from Witches Festival Grab Bags.
There is an Achievement, which is character-specific, for using 10 skeletal marionette parts to actually get the Skeletal Marionette collectible.
However it is only possible for ONE toon on any account (which may have multiple toons) to actually get this achievement, because it stops being possible to get the parts once you have the collectible. And if you have the collectible, even if you bought some parts out of the mall (before their price went astronomically insane because all the old ones were bought out, and all the new ones are account-bound), you still can't use 10 parts if you already have the Marionette.
So I propose that the Achievement in question should change, to "using the Skeletal Marionette collectible". This would make it obtainable on every character on an account, once the collectible had been obtained by the first such character.