Now, Band says you can play it (put it into play and follow the instructions) as if it were another Action card. However, we have not answered -when- Band becomes the other card. Based on the card itself, it is not that other card until it is in the play area. This tells me that if anything triggers "in your hand" it will only see the Band of Misfits and not some other card. The same can be said if an Attack triggers players to reveal their hand and discard a card costing $5 or more. Band cannot make itself "immune" to the attack by pretending it's a Young Witch.
So my answer is: No.
I disagree. Band of Misfits becomes the other card in the act of playing it. The Young Witch example is irrelevant -- we are talking about
playing BoM, not when BoM is just sitting in your hand.
You say "it is not that other card until it is in the play area". Well then, when is a card in the play area? Only after you've played it? For your conclusion to make sense, this must be your assumption. But if this is the case, then consider what happens when I play BoM as
any card.
I choose to play BoM as a card.
I am now playing BoM. Since I am still playing it, it is not in the play area. Since it is not in the play area, it is not yet the card I chose.
I have played BoM. BoM is now in the play area. BoM is now the card I chose. So, the card I chose is now
in play, but by your argument, the card I chose was never
played. The card that was played was BoM. So I don't get the benefit from the card I chose at all. BoM does nothing. Ever.
I argue instead that you have to either say that BoM is the card you want it to be
during the act of playing it, or that BoM is in the playing area during that process.
Either way, BoM is whatever card it needs to be when it needs to be, so it should be playable.
That is:
I play a hypothetical card that says "You may play an Attack card". I have BoM in hand and Cutpurse is on the table.
I decide to exercise the option to play a Cutpurse.
I play BoM AS Cutpurse, and so BoM IS Cutpurse. the original card says that I can play an attack, and in the act of playing BoM it IS an attack card, so it is legal.
All this said, I think it is really easy to argue either opinion. If such a card was ever made, I think it would HAVE to be a ruling from Donald X. For a fan card, just make a ruling yourself and fix it in the future if an official ruling ever contradicts it.