Hearthpwn

Well, I played some pre-nerf cubelock and I did not incluce umbra in the list. 

Yes, you lose some burst potential with doomguard but it's also a bit greedy and requires some setting up. E.g. you need skull of the manari, a doomguard, cube and umbra to pull it off. Against aggressive decks I actually played Umbra for tempo a lot of the time because it's a pseudo-taunt card. In the end I removed Umbra from the list and added Stonehill defender instead. 

It's a solid card but not essential.