Most played cards in 8-Cast:

4 Decks
Mishra's Bauble
8 copies - 2 average
Force of Will
8 copies - 2 average
Mox Opal
8 copies - 2 average
Ancient Tomb
8 copies - 2 average
Urza's Bauble
8 copies - 2 average
Thoughtcast
8 copies - 2 average
Chalice of the Void
8 copies - 2 average
Lotus Petal
8 copies - 2 average
Seat of the Synod
8 copies - 2 average
Urza's Saga
8 copies - 2 average
Sai, Master Thopterist
7 copies - 1.75 average
Thought Monitor
7 copies - 1.75 average
Emry, Lurker of the Loch
7 copies - 1.75 average
Force of Negation
7 copies - 1.75 average
Kappa Cannoneer
6 copies - 1.5 average
Dismember
5 copies - 1.25 average
Otawara, Soaring City
4 copies - 1 average
Flusterstorm
4 copies - 1 average
Tormod's Crypt
3 copies - 0.75 average
Brazen Borrower
3 copies - 0.75 average