Most played cards in Mardu:

4 Decks
Bloodstained Mire
14 copies - 3.5 average
Smuggler's Copter
12 copies - 3 average
Concealed Courtyard
10 copies - 2.5 average
Inspiring Vantage
10 copies - 2.5 average
Toolcraft Exemplar
8 copies - 2 average
Draconic Roar
8 copies - 2 average
Battlefield Forge
8 copies - 2 average
Thraben Inspector
8 copies - 2 average
Kolaghan's Command
8 copies - 2 average
Unlicensed Disintegration
8 copies - 2 average
Scrapheap Scrounger
8 copies - 2 average
Declaration in Stone
6 copies - 1.5 average
Windswept Heath
6 copies - 1.5 average
Wooded Foothills
6 copies - 1.5 average
Fiery Impulse
6 copies - 1.5 average
Caves of Koilos
6 copies - 1.5 average
Kolaghan, the Storm's Fury
6 copies - 1.5 average
Transgress the Mind
5 copies - 1.25 average
Tormod's Crypt
5 copies - 1.25 average
Hallowed Moonlight
4 copies - 1 average