Most played cards in Red Prison:

2 Decks
Simian Spirit Guide
8 copies - 4 average
Ancient Tomb
8 copies - 4 average
Magus of the Moon
8 copies - 4 average
Blood Moon
7 copies - 3.5 average
City of Traitors
7 copies - 3.5 average
Abrade
7 copies - 3.5 average
Grafdigger's Cage
6 copies - 3 average
Ensnaring Bridge
5 copies - 2.5 average
Null Rod
5 copies - 2.5 average
Snow-Covered Mountain
5 copies - 2.5 average
Pyroblast
5 copies - 2.5 average
Leyline of the Void
4 copies - 2 average
Birgi, God of Storytelling
4 copies - 2 average
Goblin Engineer
4 copies - 2 average
Wasteland
4 copies - 2 average
Goblin Rabblemaster
4 copies - 2 average
Great Furnace
4 copies - 2 average
Pyrostatic Pillar
3 copies - 1.5 average
Shattering Spree
3 copies - 1.5 average
Chandra, Torch of Defiance
3 copies - 1.5 average