Most played cards in Marchesa, the Black Rose:

3 Decks
Watery Grave
3 copies - 1 average
Steam Vents
3 copies - 1 average
Blood Crypt
3 copies - 1 average
Urborg, Tomb of Yawgmoth
3 copies - 1 average
Brainstorm
3 copies - 1 average
Vendilion Clique
3 copies - 1 average
Underground River
3 copies - 1 average
Mana Confluence
3 copies - 1 average
Command Tower
3 copies - 1 average
Temple of Deceit
3 copies - 1 average
Sulfurous Springs
3 copies - 1 average
Graven Cairns
3 copies - 1 average
Baleful Strix
3 copies - 1 average
Shivan Reef
3 copies - 1 average
Bloodstained Mire
3 copies - 1 average
Temple of Epiphany
3 copies - 1 average
Creeping Tar Pit
3 copies - 1 average
Thoughtseize
3 copies - 1 average
Darkslick Shores
3 copies - 1 average
Dark Confidant
3 copies - 1 average