Most played cards in Mono Black:

2 Decks
Sign in Blood
8 copies - 4 average
Mutilate
7 copies - 3.5 average
Vampire Nighthawk
7 copies - 3.5 average
Desecration Demon
7 copies - 3.5 average
Duress
6 copies - 3 average
Tragic Slip
6 copies - 3 average
Doom Blade
5 copies - 2.5 average
Mutavault
5 copies - 2.5 average
Lifebane Zombie
5 copies - 2.5 average
Liliana of the Veil
4 copies - 2 average
Corrupt
4 copies - 2 average
Bloodgift Demon
3 copies - 1.5 average
Runechanter's Pike
3 copies - 1.5 average
Pithing Needle
3 copies - 1.5 average
Underworld Connections
3 copies - 1.5 average
Liliana of the Dark Realms
3 copies - 1.5 average
Gloom Surgeon
3 copies - 1.5 average
Ultimate Price
3 copies - 1.5 average
Devour Flesh
3 copies - 1.5 average
Mind Rot
2 copies - 1 average