Update: I don't know if it's unintended or just bad design, but the trader challenge needs a change. In some cases there's no way to save the trader because the bandits can attack it before it even enters your land. The only way to counter this is Beam Wizards, which are not only one of the rarest blocks, but don't even guarantee that you can save the trader. This is because Bandits deal high damage and move faster than the trader.