When you play Goatherd on your right-hand opponent's turn, I assume that "their last turn" means the turn they had before this current turn? Which, in a multiplayer game; could have been 4 turns ago? Is this correct? Or was "their last turn" their current turn if it currently is their turn?
Same goes for playing Smugglers or Treasure Hunter on your opponent's turn. I'll make a rules forum thread for this one.