Most played cards in Mono Black.:

1 Decks
Desecration Demon
4 copies - 4 average
Thoughtseize
4 copies - 4 average
Mutavault
4 copies - 4 average
Overgrown Tomb
4 copies - 4 average
Temple of Malady
4 copies - 4 average
Hero's Downfall
4 copies - 4 average
Duress
4 copies - 4 average
Underworld Connections
4 copies - 4 average
Pack Rat
4 copies - 4 average
Gray Merchant of Asphodel
4 copies - 4 average
Nightveil Specter
3 copies - 3 average
Lifebane Zombie
3 copies - 3 average
Abrupt Decay
3 copies - 3 average
Erebos, God of the Dead
2 copies - 2 average
Pharika's Cure
2 copies - 2 average
Golgari Charm
2 copies - 2 average
Bile Blight
2 copies - 2 average
Doom Blade
2 copies - 2 average
Devour Flesh
2 copies - 2 average
Ultimate Price
1 copies - 1 average