Most played cards in Mono Black Control:

2 Decks
Tendrils of Corruption
8 copies - 4 average
Black Knight
8 copies - 4 average
Vampire Hexmage
8 copies - 4 average
Vampire Nighthawk
8 copies - 4 average
Gatekeeper of Malakir
8 copies - 4 average
Sign in Blood
8 copies - 4 average
Deathmark
7 copies - 3.5 average
Duress
7 copies - 3.5 average
Disfigure
7 copies - 3.5 average
Mind Sludge
6 copies - 3 average
Malakir Bloodwitch
6 copies - 3 average
Verdant Catacombs
4 copies - 2 average
Marsh Flats
4 copies - 2 average
Consume Spirit
4 copies - 2 average
4 copies - 2 average
Ob Nixilis, the Fallen
3 copies - 1.5 average
Marsh Casualties
3 copies - 1.5 average
Corrupt
3 copies - 1.5 average
Infest
3 copies - 1.5 average
Armillary Sphere
3 copies - 1.5 average