Most played cards in 8 Cast:

3 Decks
Urza's Bauble
12 copies - 4 average
Mox Opal
12 copies - 4 average
Mishra's Bauble
12 copies - 4 average
Emry, Lurker of the Loch
12 copies - 4 average
Seat of the Synod
12 copies - 4 average
Force of Negation
12 copies - 4 average
Urza's Saga
12 copies - 4 average
Lotus Petal
12 copies - 4 average
Ancient Tomb
12 copies - 4 average
Force of Will
12 copies - 4 average
Thought Monitor
12 copies - 4 average
Sai, Master Thopterist
12 copies - 4 average
Thoughtcast
12 copies - 4 average
Chalice of the Void
10 copies - 3.33 average
Snow-Covered Island
6 copies - 2 average
Dismember
6 copies - 2 average
Engineered Explosives
5 copies - 1.67 average
Lion's Eye Diamond
5 copies - 1.67 average
Echo of Eons
5 copies - 1.67 average
Pithing Needle
5 copies - 1.67 average