If Secret Chamber is the Bane, do you have to do top-deck-fiddly if you reveal it? Same question with Beggar and Horse Traders re: their thing.
You choose which part you want to reveal for. The timing is different anyway. It goes like this:
Alice plays Young Witch.
Bob may now reveal a Reaction that reacts to opponent playing an attack card. If he does so, resolve the reaction.
Alice draws 2 cards then discards 2 cards.
If Bob did not stop the attack (i.e. with Moat or Lighthouse), Bob may now reveal the Bane. **
If he does not reveal the Bane (and the attack was not stopped), he gains a Curse.
When Bob gains a Curse, he may reveal other reactions (i.e. Watchtower or Trader).
** I'm actually not sure about this. If you revealed Moat, can you still reveal the Bane when it comes time for it? Not that there is any reason to do so, but can you? I don't think so, because you are no longer affected by the attack.