Most played cards in All Spells:

4 Decks
Pact of Negation
16 copies - 4 average
Leyline of the Void
16 copies - 4 average
Sea Gate Restoration
16 copies - 4 average
Balustrade Spy
16 copies - 4 average
Chrome Mox
16 copies - 4 average
Dark Ritual
16 copies - 4 average
Force of Will
16 copies - 4 average
Narcomoeba
16 copies - 4 average
Agadeem's Awakening
16 copies - 4 average
Undercity Informer
16 copies - 4 average
Goblin Charbelcher
14 copies - 3.5 average
Slaughter Pact
10 copies - 2.5 average
Echoing Truth
8 copies - 2 average
Chain of Vapor
8 copies - 2 average
Cabal Therapy
7 copies - 1.75 average
Force of Negation
6 copies - 1.5 average
Mox Jet
4 copies - 1 average
Mox Emerald
4 copies - 1 average
Mox Sapphire
4 copies - 1 average
Mana Crypt
4 copies - 1 average