It is quite impossible to win if a second Hill Troll comes out in the first 1-2 rounds.
As it is quite impossible to defeat twice the Nazgul, if you can't managed the reshuffling of the Encounter deck.
So, why didn't the rules add the Unique keywords on these? It would mean that you have the same chances to find the Hill troll (2 copies) but if one is already in, you discard the second and draw a second encounter.
what do you think?
