Most played cards in Mardu:

3 Decks
Marsh Flats
12 copies - 4 average
Bloodstained Mire
10 copies - 3.33 average
Lingering Souls
9 copies - 3 average
Thoughtseize
8 copies - 2.67 average
Badlands
7 copies - 2.33 average
Scrubland
7 copies - 2.33 average
Cabal Therapy
7 copies - 2.33 average
Faithless Looting
7 copies - 2.33 average
Lightning Bolt
6 copies - 2 average
Arid Mesa
6 copies - 2 average
Hymn to Tourach
5 copies - 1.67 average
Path to Exile
5 copies - 1.67 average
Wear // Tear
5 copies - 1.67 average
Leyline of the Void
4 copies - 1.33 average
Bloodghast
4 copies - 1.33 average
Young Pyromancer
4 copies - 1.33 average
Mishra's Bauble
4 copies - 1.33 average
Dark Confidant
4 copies - 1.33 average
Priest of Forgotten Gods
4 copies - 1.33 average
Zealous Persecution
4 copies - 1.33 average