Mono Black Control has a couple of issues. Its lack of stack interaction gives it a hard time against Mulldrifter decks, while its slow, ponderous game plan makes it easy prey for Tron. At the same time, its matchups against decks like Affinity and Goblins are lackluster, despite conventional wisdom about midrange beating aggro.
Adding Red to the deck gives many advantages. Thermo Alchemist + direct damage means that you have a shot at racing Tron decks, and Pyroblast/Gorilla Shaman out of the side give you play in a lot of normally awful matchups. Additionally, you can utilize the passive card advantage and life gain afforded by dual color mana bases.
Thorn of the Black Rose has been excellent in testing, particularly against Tron. While it seems lackluster against aggro, and does ocassionally sit dead in the hand, I've had just as many games in which it's been instrumental in turning the corner against faster decks.
Current sideboard plans: side into a disruptive burn deck vs. Tron with Pyroblast and Blightning over some combination of Chainer's, Flame Slash, Dead Weight and Terminate. Against Burn, you're basically hoping to stick a Grotesque Mutation on something big and race them (picking up a Radiant Fountain a few times doesn't hurt either). Against Stompy and other go wide decks, you have Electrickeries, as well as Grotesque Mutation + Crypt Rats to clear the board and stabilize your life at the same time. Against Affinity, hope to draw an early Gorilla Shaman and collect free wins.
