Most played cards in Mono-Black Eldrazi:

2 Decks
Thought-Knot Seer
8 copies - 4 average
Bearer of Silence
8 copies - 4 average
Reality Smasher
8 copies - 4 average
Shrine of the Forsaken Gods
8 copies - 4 average
Transgress the Mind
8 copies - 4 average
Ruinous Path
8 copies - 4 average
Wasteland Strangler
8 copies - 4 average
Matter Reshaper
6 copies - 3 average
Languish
5 copies - 2.5 average
Sea Gate Wreckage
5 copies - 2.5 average
Titan's Presence
5 copies - 2.5 average
Oblivion Sower
5 copies - 2.5 average
Distended Mindbender
5 copies - 2.5 average
Caves of Koilos
4 copies - 2 average
Blighted Fen
4 copies - 2 average
Mirrorpool
3 copies - 1.5 average
Eldrazi Mimic
3 copies - 1.5 average
Ulamog, the Ceaseless Hunger
3 copies - 1.5 average
Endless One
3 copies - 1.5 average
Grasp of Darkness
2 copies - 1 average