Most played cards in 8 Cast:

2 Decks
Thoughtcast
8 copies - 4 average
Force of Will
8 copies - 4 average
Seat of the Synod
8 copies - 4 average
Urza's Saga
8 copies - 4 average
Hurkyl's Recall
8 copies - 4 average
Thought Monitor
8 copies - 4 average
Flusterstorm
8 copies - 4 average
Soul-Guide Lantern
6 copies - 3 average
Mox Opal
6 copies - 3 average
Pithing Needle
5 copies - 2.5 average
Urza, Lord High Artificer
4 copies - 2 average
Urza's Bauble
4 copies - 2 average
Dismember
4 copies - 2 average
Mishra's Bauble
4 copies - 2 average
Mystical Dispute
4 copies - 2 average
Emry, Lurker of the Loch
3 copies - 1.5 average
Time Walk
2 copies - 1 average
Time Vault
2 copies - 1 average
Sea Gate Restoration
2 copies - 1 average
Tolarian Academy
2 copies - 1 average