Most played cards in Rielle, the Everwise:

3 Decks
Snow-Covered Island
17 copies - 5.67 average
Snow-Covered Mountain
12 copies - 4 average
Flame Slash
3 copies - 1 average
Firestorm
3 copies - 1 average
Force Spike
3 copies - 1 average
Force of Will
3 copies - 1 average
Izzet Charm
3 copies - 1 average
Frantic Search
3 copies - 1 average
Fiery Temper
3 copies - 1 average
Force of Negation
3 copies - 1 average
Faithless Looting
3 copies - 1 average
Chain Lightning
3 copies - 1 average
Brainstorm
3 copies - 1 average
Abrade
3 copies - 1 average
Conflagrate
3 copies - 1 average
Counterspell
3 copies - 1 average
Lightning Bolt
3 copies - 1 average
Deflecting Swat
3 copies - 1 average
Cryptic Command
3 copies - 1 average
Arid Mesa
3 copies - 1 average