Most played cards in U/B Beats:

2 Decks
Moroii
8 copies - 4 average
Cruel Edict
8 copies - 4 average
Watery Grave
8 copies - 4 average
Necroplasm
8 copies - 4 average
Umezawa's Jitte
8 copies - 4 average
Hypnotic Specter
8 copies - 4 average
Dimir Cutpurse
8 copies - 4 average
Rend Flesh
7 copies - 3.5 average
Underground River
7 copies - 3.5 average
Nekrataal
7 copies - 3.5 average
Dark Banishing
5 copies - 2.5 average
Nezumi Graverobber
4 copies - 2 average
Mana Leak
4 copies - 2 average
Last Gasp
4 copies - 2 average
Tendo Ice Bridge
4 copies - 2 average
Jushi Apprentice
4 copies - 2 average
Ink-Eyes, Servant of Oni
4 copies - 2 average
Tempest of Light
4 copies - 2 average
Dark Confidant
4 copies - 2 average
Pithing Needle
3 copies - 1.5 average