It's not clear to me how Panther would interact with Watchtower or Transmogrify. Which one takes precedence?
If you are gaining a card, then you can choose which to reveal. If you reveal Watchtower, then revealing Panther won't do anything, because it will have lost track. If you reveal Panther, then lose track will make Watchtower do nothing.
If your opponent gains a card, then he has the right to reveal Watchtower before you have the right to reveal Panther. If he does, then your Panther won't do anything because of lose track.
Transmogrify wouldn't have any interaction with it. It gains a card to hand, after which Panther could be revealed to place the card on top of the deck. Lose track doesn't apply because it is gained directly to hand, not moved to hand by a separate effect. In practice this could be a minor issue for real life play; as the card is technically already in your opponent's hand when you reveal Panther, so how can you know your opponent put the right card back? I don't think it's a real problem though, as you'll reveal Panther as your opponent grabs the victory card from transmogrify.