The National Dex Monotype council has chosen to quickban Shed Tail!
Shed Tail's ability to facilitate powerful sweepers like Ursaluna-BM, Kommo-o, and Gouging Fire proves to be too much for the National Dex Monotype metagame. This is further exemplified by Terapagos' introduction, whose ability ensures that the substitute passed will not be broken in one hit. Aside from providing a safe entry for these sweepers, Shed Tail also bypasses common ways to deal with these threats and allows them to have an extra move for coverage or more setup. For instance, Toxapex can threaten out Gouging Fire with Toxic, as the aforementioned Dragon is unable to eliminate Toxapex in one hit, or Choice Scarf Meowscarada can easily revenge-kill Kommo-o lacking Vacuum Wave if not for Shed Tail protecting Kommo-o.
It may seem that it's all Cyclizar's fault, as all of the sweepers mentioned so far are his teammates, but Steel teams can use Othworm to facilitate sweepers like Gholdengo better. Because of this, the council opted to do away with the move instead of the Pokemon itself.
Tagging Kris to implement.