Most played cards in Rock:

1 Decks
Naturalize
4 copies - 4 average
Pernicious Deed
4 copies - 4 average
Cabal Therapy
4 copies - 4 average
Treetop Village
4 copies - 4 average
Llanowar Wastes
4 copies - 4 average
Wall of Blossoms
4 copies - 4 average
Ravenous Baloth
4 copies - 4 average
Duress
4 copies - 4 average
City of Brass
3 copies - 3 average
Kavu Titan
3 copies - 3 average
Engineered Plague
2 copies - 2 average
Cursed Totem
2 copies - 2 average
Plague Spitter
2 copies - 2 average
Spike Feeder
2 copies - 2 average
Tormod's Crypt
2 copies - 2 average
Hystrodon
2 copies - 2 average
Vendetta
2 copies - 2 average
Recurring Nightmare
2 copies - 2 average
Dust Bowl
2 copies - 2 average
Smother
2 copies - 2 average