Well, it's kind of Gravedigger and the Stronghold (potentionally) working together - Stronghold brings back Gravedigger, Gravedigger brings back another creature, and that can keep happening as long as Stronghold is in play. In other words, by themselves, Gravedigger is a one-time shot but Stronghold can just keep going and going... so I think that's the bigger threat right now, even if it didn't necessary get going all the way during the game (it might have had it lasted longer and I didn't put out Last Laugh).