Most played cards in Opposition:

3 Decks
Birds of Paradise
12 copies - 4 average
Yavimaya Coast
12 copies - 4 average
Wall of Roots
10 copies - 3.33 average
Opposition
10 copies - 3.33 average
Chill
8 copies - 2.67 average
Survival of the Fittest
8 copies - 2.67 average
Llanowar Elves
8 copies - 2.67 average
Naturalize
8 copies - 2.67 average
Hydroblast
7 copies - 2.33 average
Winter Orb
6 copies - 2 average
Wall of Blossoms
6 copies - 2 average
City of Brass
5 copies - 1.67 average
Merfolk Looter
4 copies - 1.33 average
Gaea's Cradle
4 copies - 1.33 average
Tangle Wire
4 copies - 1.33 average
Wasteland
4 copies - 1.33 average
Mana Leak
4 copies - 1.33 average
Counterspell
4 copies - 1.33 average
Accumulated Knowledge
4 copies - 1.33 average
Tormod's Crypt
4 copies - 1.33 average