Halloween Pets such as the Witch Hat Charlotte and Neurotic Cabby can only be exchanged with other Halloween Pets and it will not be possible to exchange these pets with other Cats.
*All Halloween Pets can be exchanged with eachother. For example, you can exchange a Drifty Ghosphy with a Cursed Looney.*
Crows can only be exchanged with other Crows, since different breeds of birds are not the same species.
For example, you will not be able to exchange a Crow with a Hawk.
*Although the Crow was released for the Halloween update it is not considered a Halloween Pet so you will not have the ability to exchange it with Halloween Pets.*