Most played cards in Mono Black:

4 Decks
Dread Wanderer
16 copies - 4 average
Fatal Push
14 copies - 3.5 average
Glint-Sleeve Siphoner
12 copies - 3 average
Duress
12 copies - 3 average
Gifted Aetherborn
12 copies - 3 average
Scrapheap Scrounger
12 copies - 3 average
Night Market Lookout
12 copies - 3 average
Vicious Conquistador
11 copies - 2.75 average
Aether Hub
11 copies - 2.75 average
Lightning Strike
8 copies - 2 average
Dragonskull Summit
8 copies - 2 average
Ifnir Deadlands
8 copies - 2 average
Doomfall
6 copies - 1.5 average
Yahenni, Undying Partisan
6 copies - 1.5 average
Aethersphere Harvester
6 copies - 1.5 average
Hazoret the Fervent
6 copies - 1.5 average
Bontu's Last Reckoning
5 copies - 1.25 average
Lord of the Accursed
4 copies - 1 average
Liliana's Mastery
4 copies - 1 average
Diregraf Colossus
4 copies - 1 average