Most played cards in UBR:

1 Decks
Mishra's Factory
4 copies - 4 average
Volcanic Island
4 copies - 4 average
Strip Mine
4 copies - 4 average
Lightning Bolt
4 copies - 4 average
Underground Sea
4 copies - 4 average
Red Elemental Blast
4 copies - 4 average
Blue Elemental Blast
4 copies - 4 average
Sedge Troll
4 copies - 4 average
Counterspell
4 copies - 4 average
Nevinyrral's Disk
4 copies - 4 average
City of Brass
3 copies - 3 average
Power Sink
3 copies - 3 average
Badlands
2 copies - 2 average
Mind Control
2 copies - 2 average
Shatterstorm
2 copies - 2 average
City in a Bottle
2 copies - 2 average
Amnesia
2 copies - 2 average
Library of Alexandria
1 copies - 1 average
Sol Ring
1 copies - 1 average
Mana Drain
1 copies - 1 average