Riverboat, it's like Mastermind/King's Court, except with any $5 non-duration.
Oh the silliness that can happen.
Way of the Mouse->Riverboat->Band of Misfits->something else->Way of the Mouse
But at least that isn't infinite, due to Riverboat's delay.
Otherwise, put Small Castle, Royal Carriage, or Distant Lands on your riverboat for silliness.
OR: Wine Merchant becomes absolutely amazing when he can't go to the Tavern.
Most of the Knights could be placed on it, some better than others.
Hero and Disciple are excellent. Cursed Village will only draw 1 most of the time, but could be nice in hand-attack kingdoms.
I assume that if Pooka is riding the riverboat that all players get Cursed Gold.
First Mate at the start of a turn without costing an action is another fun idea.
I'm looking forward to seeing the recommended kingdoms in the rulebook.