Your minions trigger their Deathrattles twice.
There used to be five Horsemen but one of them left because a job opened up in the deadmines and the benefits were better.
Deathrattle - Does something when it dies.
How to Unlock Baron Rivendare
Unlocked in The Military Quarter, in the Naxxramas adventure.
How to Unlock Golden Baron Rivendare
Crafting unlocked in The Military Quarter, in the Naxxramas adventure.