So, if I play this with Gallows out, and then my opponent plays this as well, I can play this a second time via TSC now that its in my discard pile.
I'm not so much worried about this acting as a counter against "remove all cards in battle from the game" type cards, but I am worried about how returning cards that were removed from the game may create imbalances on cards that are removed from the game as part of their cost to balance them. Such as, ANB, The Flood, Pharaoh's Baker, Confusion, and I'm sure many others. In fact, if your running Gallows anyways, you would be able to play Haman's Plot 8 times in a Type-2 game.
I'm not trying to be overly critical, just pointing out that this card has some crazy combo potential.