Most played cards in Sun and Moon:

4 Decks
Chalice of the Void
16 copies - 4 average
Blood Moon
16 copies - 4 average
Nahiri, the Harbinger
16 copies - 4 average
Arid Mesa
15 copies - 3.75 average
Lightning Helix
15 copies - 3.75 average
Temple of Triumph
15 copies - 3.75 average
Simian Spirit Guide
14 copies - 3.5 average
Anger of the Gods
13 copies - 3.25 average
Rest in Peace
12 copies - 3 average
Leyline of Sanctity
11 copies - 2.75 average
Wrath of God
10 copies - 2.5 average
Seasoned Pyromancer
8 copies - 2 average
Sacred Foundry
8 copies - 2 average
Sunbaked Canyon
8 copies - 2 average
Gemstone Caverns
7 copies - 1.75 average
Stony Silence
7 copies - 1.75 average
Rugged Prairie
6 copies - 1.5 average
Cast Out
5 copies - 1.25 average
Gideon Jura
5 copies - 1.25 average
Ensnaring Bridge
5 copies - 1.25 average