Most played cards in Mono Black:

1 Decks
Hypnotic Specter
4 copies - 4 average
Dark Ritual
4 copies - 4 average
Carnophage
4 copies - 4 average
Duress
4 copies - 4 average
Mishra's Factory
4 copies - 4 average
Dauthi Horror
4 copies - 4 average
Dauthi Slayer
4 copies - 4 average
Mesmeric Fiend
4 copies - 4 average
Cabal Therapy
3 copies - 3 average
Engineered Plague
2 copies - 2 average
Planar Void
2 copies - 2 average
Withered Wretch
2 copies - 2 average
Smother
2 copies - 2 average
Diabolic Edict
2 copies - 2 average
Perish
2 copies - 2 average
Foul Imp
2 copies - 2 average
Nevinyrral's Disk
2 copies - 2 average
Nantuko Shade
2 copies - 2 average
Sinister Strength
2 copies - 2 average
Skeletal Scrying
2 copies - 2 average