Most played cards in Mono Blue:

1 Decks
Delver of Secrets
4 copies - 4 average
Daze
4 copies - 4 average
Force of Will
4 copies - 4 average
Wasteland
4 copies - 4 average
Brainstorm
4 copies - 4 average
Ponder
4 copies - 4 average
Leyline of the Void
3 copies - 3 average
Preordain
3 copies - 3 average
Gut Shot
3 copies - 3 average
Scalding Tarn
3 copies - 3 average
Polluted Delta
3 copies - 3 average
True-Name Nemesis
3 copies - 3 average
Ethereal Forager
3 copies - 3 average
Stormwing Entity
3 copies - 3 average
Divert
2 copies - 2 average
Misty Rainforest
2 copies - 2 average
Grafdigger's Cage
2 copies - 2 average
Back to Basics
2 copies - 2 average
Snap
2 copies - 2 average
Force of Negation
2 copies - 2 average