Most played cards in Merfolks:

2 Decks
Cavern of Souls
8 copies - 4 average
Silvergill Adept
8 copies - 4 average
Force of Will
8 copies - 4 average
Master of the Pearl Trident
8 copies - 4 average
Mental Misstep
8 copies - 4 average
Lord of Atlantis
8 copies - 4 average
Wasteland
8 copies - 4 average
Cursecatcher
8 copies - 4 average
Null Rod
6 copies - 3 average
Grafdigger's Cage
6 copies - 3 average
True-Name Nemesis
6 copies - 3 average
Tormod's Crypt
5 copies - 2.5 average
Dismember
4 copies - 2 average
Hurkyl's Recall
4 copies - 2 average
Flooded Strand
4 copies - 2 average
Mindbreak Trap
3 copies - 1.5 average
Phantasmal Image
3 copies - 1.5 average
Merrow Reejerey
3 copies - 1.5 average
Karakas
2 copies - 1 average
Steel Sabotage
2 copies - 1 average