Object art by Kyle Merritt.
Background art by David Nyari.
Like any card with an activated ability, this card's effect must be played during the Build phase before Rooms are revealed. So it cannot affect the Bait phase until the turn after it is played.
Jackpot Stash only doubles treasure from other Rooms, not Boss cards or other effects.
It effects all active Rooms in your dungeon, including any Room revealed when Jackpot Stash is destroyed.
While the card effect can be risky, it pays off to be able to either lure a Hero away into your dungeon, or to even keep a Hero in town for a turn. It might not be recommended to use the effect of this card when Epic Heroes start coming into play, as it might result in the quick build up of Wounds (or Souls, if one is properly prepared).
The painting in the art resembles the Mona Lisa.