Most played cards in Gruul:

6 Decks
Lightning Bolt
20 copies - 3.33 average
Soul-Scar Mage
20 copies - 3.33 average
Copperline Gorge
20 copies - 3.33 average
Monastery Swiftspear
20 copies - 3.33 average
Stomping Ground
17 copies - 2.83 average
Mishra's Bauble
16 copies - 2.67 average
Seal of Fire
16 copies - 2.67 average
Manamorphose
16 copies - 2.67 average
Wooded Foothills
16 copies - 2.67 average
Tarmogoyf
16 copies - 2.67 average
Light Up the Stage
16 copies - 2.67 average
Lava Dart
16 copies - 2.67 average
Hooting Mandrills
12 copies - 2 average
Arid Mesa
10 copies - 1.67 average
Klothys, God of Destiny
9 copies - 1.5 average
Abbot of Keral Keep
8 copies - 1.33 average
Tormod's Crypt
8 copies - 1.33 average
Flame Slash
8 copies - 1.33 average
Abrade
8 copies - 1.33 average
Scalding Tarn
7 copies - 1.17 average