Most played cards in Monster Mash:

1 Decks
Swords to Plowshares
4 copies - 4 average
City of Brass
4 copies - 4 average
Birds of Paradise
4 copies - 4 average
Savannah
4 copies - 4 average
Lightning Bolt
4 copies - 4 average
Plateau
4 copies - 4 average
Disenchant
4 copies - 4 average
Serra Angel
3 copies - 3 average
Mana Vault
3 copies - 3 average
Mishra's Factory
3 copies - 3 average
Whirling Dervish
3 copies - 3 average
Red Elemental Blast
3 copies - 3 average
Giant Spider
3 copies - 3 average
Erhnam Djinn
2 copies - 2 average
Tsunami
2 copies - 2 average
Tranquility
2 copies - 2 average
Taiga
2 copies - 2 average
Shivan Dragon
2 copies - 2 average
Earthquake
2 copies - 2 average
Fireball
1 copies - 1 average