Most played cards in U/R Delver:

8 Decks
Brainstorm
8 copies - 1 average
Murktide Regent
8 copies - 1 average
Dragon's Rage Channeler
8 copies - 1 average
Expressive Iteration
8 copies - 1 average
Lightning Bolt
8 copies - 1 average
Pyroblast
8 copies - 1 average
Ponder
8 copies - 1 average
Wasteland
8 copies - 1 average
Force of Will
8 copies - 1 average
Volcanic Island
8 copies - 1 average
Daze
6 copies - 0.75 average
Mishra's Bauble
6 copies - 0.75 average
Delver of Secrets
5 copies - 0.63 average
Meltdown
4 copies - 0.5 average
Flooded Strand
4 copies - 0.5 average
Leyline of the Void
4 copies - 0.5 average
Misty Rainforest
4 copies - 0.5 average
Scalding Tarn
4 copies - 0.5 average
Polluted Delta
4 copies - 0.5 average
Force of Negation
3 copies - 0.38 average