Played a Spriritsinger Umbra with a Kel’Thuzad on board. Then played a Greybough and nothing happened with its deathrattle.
Windows 10
Kel’Thuzad has an end-of-turn effect that resummons all of the friendly minions that died during the turn. But according to your description, no minions died, so Kel’Thuzad’s effect didn’t do anything. What were you expecting to happen?
Greybough’s deathrattle doesn’t summon anything – it gives a new deathrattle to a random friendly minion.
What were you expecting to happen? Did you check your other minions to see if they gained the new deathrattle?