Most played cards in MonoU Tempo:

1 Decks
Chalice of the Void
4 copies - 4 average
Force of Negation
4 copies - 4 average
Dismember
4 copies - 4 average
Subtlety
4 copies - 4 average
Misty Rainforest
4 copies - 4 average
Counterspell
4 copies - 4 average
Spreading Seas
4 copies - 4 average
Hall of Storm Giants
4 copies - 4 average
Tide Shaper
4 copies - 4 average
Ratchet Bomb
3 copies - 3 average
Vendilion Clique
3 copies - 3 average
Svyelun of Sea and Sky
3 copies - 3 average
Brazen Borrower
3 copies - 3 average
Cemetery Illuminator
2 copies - 2 average
Dress Down
2 copies - 2 average
Hurkyl's Recall
2 copies - 2 average
Blast Zone
2 copies - 2 average
Otawara, Soaring City
2 copies - 2 average
Unlicensed Hearse
2 copies - 2 average
Thirst of Knowledge
2 copies - 2 average