I finished the quest line and then all challenges.
Upon finishing the last challenge, I received the hammer of urskaya as a reward (hero weapon).
My wife did the exact same thing as me, she didn't get the hammer.
Does anyone know what triggers the reward?
Is it just a random drop chance after a fight?
This might be related to dinging after you finish the questline, as my wife got it when she dinged a few matches later.