Most played cards in MUD:

2 Decks
Ancient Tomb
8 copies - 4 average
Metalworker
8 copies - 4 average
City of Traitors
8 copies - 4 average
Wasteland
8 copies - 4 average
Rishadan Port
8 copies - 4 average
Masticore
8 copies - 4 average
Mishra's Factory
8 copies - 4 average
Mind Stone
8 copies - 4 average
Powder Keg
5 copies - 2.5 average
Mox Diamond
4 copies - 2 average
Mishra's Helix
4 copies - 2 average
Goblin Welder
4 copies - 2 average
Avalanche Riders
4 copies - 2 average
Sphere of Resistance
4 copies - 2 average
Thran Dynamo
4 copies - 2 average
Karn, Silver Golem
4 copies - 2 average
Tangle Wire
4 copies - 2 average
Urza's Bauble
4 copies - 2 average
Stone Rain
4 copies - 2 average
Ensnaring Bridge
3 copies - 1.5 average