Mercenaries work well, if you have the cards and the style. The key is mana and speed. I suggest bog witch and throw in undertakers. Also, I faced a nasty mercenary/rebel conspiracy deck. I personally prefer rebels, especially now that Lin Sivvi is printed (Enduring renewal makes lin sivvi god!!!) I find that black swarm decks are somewhat lacking with mercenaries, so keep speed in the beginning and never let up on the pressure if you can. They good ones are excellent, but the bad ones are really bad.
