Most played cards in Mardu:

4 Decks
Doom Foretold
12 copies - 3 average
Bloodchief's Thirst
10 copies - 2.5 average
Tymaret Calls the Dead
8 copies - 2 average
Bonecrusher Giant
8 copies - 2 average
Kroxa, Titan of Death's Hunger
8 copies - 2 average
Skyclave Shade
8 copies - 2 average
Treacherous Blessing
7 copies - 1.75 average
Heartless Act
7 copies - 1.75 average
Duress
6 copies - 1.5 average
Shatterskull Smashing
6 copies - 1.5 average
Extinction Event
6 copies - 1.5 average
Agonizing Remorse
5 copies - 1.25 average
Elspeth's Nightmare
5 copies - 1.25 average
Skyclave Apparition
4 copies - 1 average
Hagra Mauling
4 copies - 1 average
The Birth of Meletis
4 copies - 1 average
Glass Casket
4 copies - 1 average
Mazemind Tome
4 copies - 1 average
Brightclimb Pathway
4 copies - 1 average
Fabled Passage
4 copies - 1 average