Most played cards in Mono Black Control:

3 Decks
Duress
12 copies - 4 average
Snow-Covered Swamp
12 copies - 4 average
Engineered Plague
10 copies - 3.33 average
Nether Spirit
10 copies - 3.33 average
Innocent Blood
9 copies - 3 average
Contamination
8 copies - 2.67 average
Zombie Infestation
8 copies - 2.67 average
Wasteland
8 copies - 2.67 average
Dystopia
8 copies - 2.67 average
Mishra's Factory
8 copies - 2.67 average
Rishadan Port
8 copies - 2.67 average
Cabal Therapy
8 copies - 2.67 average
Skeletal Scrying
6 copies - 2 average
Nevinyrral's Disk
6 copies - 2 average
Diabolic Edict
5 copies - 1.67 average
Sickening Dreams
4 copies - 1.33 average
Null Rod
4 copies - 1.33 average
Phyrexian Arena
4 copies - 1.33 average
Diabolic Tutor
4 copies - 1.33 average
Perish
4 copies - 1.33 average