Most played cards in Red Prison:

3 Decks
Magus of the Moon
12 copies - 4 average
Simian Spirit Guide
12 copies - 4 average
Ancient Tomb
12 copies - 4 average
Blood Moon
11 copies - 3.67 average
City of Traitors
11 copies - 3.67 average
Abrade
7 copies - 2.33 average
Grafdigger's Cage
7 copies - 2.33 average
Null Rod
6 copies - 2 average
Goblin Rabblemaster
6 copies - 2 average
Ensnaring Bridge
6 copies - 2 average
Shattering Spree
6 copies - 2 average
Pyroblast
5 copies - 1.67 average
Snow-Covered Mountain
5 copies - 1.67 average
Chandra, Torch of Defiance
5 copies - 1.67 average
Leyline of the Void
4 copies - 1.33 average
Wasteland
4 copies - 1.33 average
Birgi, God of Storytelling
4 copies - 1.33 average
Goblin Engineer
4 copies - 1.33 average
Ragavan, Nimble Pilferer
4 copies - 1.33 average
Scab-Clan Berserker
4 copies - 1.33 average