You can be awful to Faith if you like. She'll be cursed without her slayer powers, and I can give you some near-future stuff to torture her for, though the past stuff is always good to dredge up and use to make her feel like garbage...

Same for Donna, if you want. She is just post metacrisis, but she's not Doctor Donna'd out, obviously.

And of course Cas is fair game, but I don't want to spoil you so if you'd rather just mess with his Future Self's potential future, I'm down.