There's an issue: because of arceus, any attempt to type change is impossible other than trick or treat and forest's curse. Because there is an arceus of every type, and no two move combo can hit all single types se, you can't just run appropriate coverage on type changing. There is also no three type combination that hits all existing mons for super effective damage. Therefore, the only possible methods much involve trick or treat or forest's curse. However, its pretty simple to determine that no 2 move coverage can hit all mons w/ ghost type tacked on (any normal mon beats you unless you have dark coverage, with dark coverage you need a move to hit fairies, and you need a move to hit darks, and no type hits both). Forest's curse is in a similar boat, where only flying has all its resists weak to one type, and that one type is ground, so mons like archeops and skarmory can not be hit for se
So its 100% impossible w/ arceus formes allowed
EDIT: molk pointed out on the second page we were told no plates were allowed, so that fixes this