Most played cards in RU:

1 Decks
Shatter
4 copies - 4 average
Chain Lightning
4 copies - 4 average
Psionic Blast
4 copies - 4 average
Mishra's Factory
4 copies - 4 average
Black Vise
4 copies - 4 average
Counterspell
4 copies - 4 average
Lightning Bolt
4 copies - 4 average
Volcanic Island
4 copies - 4 average
Maze of Ith
3 copies - 3 average
Red Elemental Blast
3 copies - 3 average
Blue Elemental Blast
3 copies - 3 average
Hurkyl's Recall
2 copies - 2 average
Ball Lightning
2 copies - 2 average
City of Brass
2 copies - 2 average
City in a Bottle
2 copies - 2 average
Timetwister
1 copies - 1 average
Wheel of Fortune
1 copies - 1 average
Library of Alexandria
1 copies - 1 average
Earthquake
1 copies - 1 average
Hammerheim
1 copies - 1 average