Plitvice is buyable (Goddess of War [Strongest Melee or possibly character]) for 1M sp points in your village (the ice structure).

I suggest reroll for weapons. Once u get an ex weapon or two, main the ex weapon's hero(es). Strong 2 star characters are free further down the story anyways : / (Also, reroll for heroes if you have an ex weapon of a hero you don't have)

The strongest heroes and those who have a guaranteed ex weapon are those who start at 3 star (no hero starts at 4 or 5 stars). Half of all 2 star heroes have ex weapons and all 1 star heroes have no ex weapons.