Most played cards in Combo:

2 Decks
Badlands
4 copies - 2 average
Hypnotic Specter
4 copies - 2 average
Sinkhole
4 copies - 2 average
Underworld Dreams
4 copies - 2 average
Underground Sea
4 copies - 2 average
Sedge Troll
4 copies - 2 average
Volcanic Island
4 copies - 2 average
Lightning Bolt
4 copies - 2 average
Gloom
3 copies - 1.5 average
Terror
3 copies - 1.5 average
Dark Ritual
3 copies - 1.5 average
Juzám Djinn
3 copies - 1.5 average
Drain Life
2 copies - 1 average
Greed
2 copies - 1 average
City of Brass
2 copies - 1 average
Red Elemental Blast
2 copies - 1 average
Nevinyrral's Disk
2 copies - 1 average
Shatterstorm
2 copies - 1 average
Sol'kanar the Swamp King
2 copies - 1 average
Shatter
1 copies - 0.5 average