Most played cards in Horde of Notions:

3 Decks
Savannah
3 copies - 1 average
Watery Grave
3 copies - 1 average
Polluted Delta
3 copies - 1 average
Windswept Heath
3 copies - 1 average
Abrupt Decay
3 copies - 1 average
Steam Vents
3 copies - 1 average
Temple Garden
3 copies - 1 average
Taiga
3 copies - 1 average
Overgrown Tomb
3 copies - 1 average
Stomping Ground
3 copies - 1 average
Tropical Island
3 copies - 1 average
Plateau
3 copies - 1 average
Hallowed Fountain
3 copies - 1 average
Misty Rainforest
3 copies - 1 average
Flooded Strand
3 copies - 1 average
Badlands
3 copies - 1 average
Swords to Plowshares
3 copies - 1 average
Marsh Flats
3 copies - 1 average
Thirst for Knowledge
2 copies - 0.67 average
Arid Mesa
2 copies - 0.67 average