Most played cards in Rebels:

2 Decks
Swords to Plowshares
8 copies - 4 average
Mana Leak
8 copies - 4 average
Adarkar Wastes
8 copies - 4 average
Ramosian Sergeant
8 copies - 4 average
Lin Sivvi, Defiant Hero
7 copies - 3.5 average
Counterspell
6 copies - 3 average
Blue Elemental Blast
6 copies - 3 average
Flooded Strand
6 copies - 3 average
Defiant Falcon
5 copies - 2.5 average
Shared Triumph
5 copies - 2.5 average
Mother of Runes
4 copies - 2 average
Absorb
4 copies - 2 average
Whipcorder
4 copies - 2 average
Standstill
4 copies - 2 average
Coastal Tower
4 copies - 2 average
Disenchant
3 copies - 1.5 average
Hibernation
2 copies - 1 average
Ramosian Sky Marshal
2 copies - 1 average
Worship
2 copies - 1 average
Armageddon
2 copies - 1 average