Most played cards in Merfolks:

6 Decks
Lord of Atlantis
24 copies - 4 average
Merrow Reejerey
24 copies - 4 average
Cursecatcher
24 copies - 4 average
Cryptic Command
21 copies - 3.5 average
Path to Exile
20 copies - 3.33 average
Silvergill Adept
20 copies - 3.33 average
Wanderwine Hub
20 copies - 3.33 average
Mutavault
20 copies - 3.33 average
Umezawa's Jitte
16 copies - 2.67 average
Meddling Mage
13 copies - 2.17 average
Scalding Tarn
13 copies - 2.17 average
Hallowed Fountain
12 copies - 2 average
11 copies - 1.83 average
Threads of Disloyalty
10 copies - 1.67 average
Pithing Needle
10 copies - 1.67 average
Spell Pierce
10 copies - 1.67 average
Merfolk Sovereign
10 copies - 1.67 average
Misty Rainforest
9 copies - 1.5 average
Coralhelm Commander
8 copies - 1.33 average
Ponder
8 copies - 1.33 average