Most played cards in Merfolks:

3 Decks
Lord of Atlantis
12 copies - 4 average
Mutavault
12 copies - 4 average
Silvergill Adept
12 copies - 4 average
Spreading Seas
12 copies - 4 average
Merrow Reejerey
12 copies - 4 average
Cryptic Command
12 copies - 4 average
Cursecatcher
12 copies - 4 average
Coralhelm Commander
9 copies - 3 average
Wanderwine Hub
8 copies - 2.67 average
Glacial Fortress
8 copies - 2.67 average
Mana Leak
8 copies - 2.67 average
Merfolk Sovereign
8 copies - 2.67 average
Path to Exile
6 copies - 2 average
Relic of Progenitus
6 copies - 2 average
Vendilion Clique
5 copies - 1.67 average
Meddling Mage
4 copies - 1.33 average
Oblivion Ring
4 copies - 1.33 average
Flashfreeze
3 copies - 1 average
Tormod's Crypt
3 copies - 1 average
Ancestral Vision
3 copies - 1 average