Most played cards in Merfolks:

2 Decks
Merfolk Sovereign
8 copies - 4 average
Merrow Reejerey
8 copies - 4 average
Mutavault
8 copies - 4 average
Silvergill Adept
8 copies - 4 average
Mana Leak
8 copies - 4 average
Spreading Seas
8 copies - 4 average
Cursecatcher
8 copies - 4 average
Lord of Atlantis
8 copies - 4 average
Coralhelm Commander
8 copies - 4 average
Tectonic Edge
6 copies - 3 average
Cryptic Command
6 copies - 3 average
Meddling Mage
4 copies - 2 average
Adarkar Wastes
4 copies - 2 average
Glacial Fortress
4 copies - 2 average
Sower of Temptation
3 copies - 1.5 average
Vendilion Clique
3 copies - 1.5 average
Flashfreeze
3 copies - 1.5 average
Relic of Progenitus
3 copies - 1.5 average
Tormod's Crypt
3 copies - 1.5 average
Negate
2 copies - 1 average