Most played cards in BR Midrange:

2 Decks
Hypnotic Specter
8 copies - 4 average
Sedge Troll
8 copies - 4 average
Badlands
8 copies - 4 average
Lightning Bolt
8 copies - 4 average
Nevinyrral's Disk
6 copies - 3 average
Dark Ritual
6 copies - 3 average
Red Elemental Blast
6 copies - 3 average
Gloom
6 copies - 3 average
Mishra's Factory
5 copies - 2.5 average
Rukh Egg
5 copies - 2.5 average
Order of the Ebon Hand
4 copies - 2 average
Sinkhole
4 copies - 2 average
Hymn to Tourach
4 copies - 2 average
Animate Dead
4 copies - 2 average
Fallen Angel
3 copies - 1.5 average
Shatter
3 copies - 1.5 average
Disintegrate
3 copies - 1.5 average
City in a Bottle
3 copies - 1.5 average
Black Vise
2 copies - 1 average
Pestilence
2 copies - 1 average