Most played cards in Karn Echoes:

2 Decks
Mesmeric Orb
8 copies - 4 average
Ancient Tomb
8 copies - 4 average
Lion's Eye Diamond
8 copies - 4 average
Mox Opal
8 copies - 4 average
Mystic Forge
8 copies - 4 average
Karn, Scion of Urza
8 copies - 4 average
Voltaic Key
8 copies - 4 average
Karn, the Great Creator
8 copies - 4 average
Lotus Petal
8 copies - 4 average
Grim Monolith
8 copies - 4 average
City of Traitors
8 copies - 4 average
Echo of Eons
8 copies - 4 average
Crystal Vein
8 copies - 4 average
Defense Grid
8 copies - 4 average
Basalt Monolith
8 copies - 4 average
Inventors' Fair
6 copies - 3 average
Tormod's Crypt
6 copies - 3 average
Walking Ballista
4 copies - 2 average
Manifold Key
4 copies - 2 average
Skysovereign, Consul Flagship
2 copies - 1 average