Most played cards in Grixis:

1 Decks
Demigod of Revenge
4 copies - 4 average
Reflecting Pool
4 copies - 4 average
Anathemancer
4 copies - 4 average
Flashfreeze
4 copies - 4 average
Cryptic Command
4 copies - 4 average
Lightning Bolt
4 copies - 4 average
Cascade Bluffs
4 copies - 4 average
Crumbling Necropolis
4 copies - 4 average
Pyroclasm
3 copies - 3 average
Vivid Crag
3 copies - 3 average
Volcanic Fallout
3 copies - 3 average
Vivid Creek
3 copies - 3 average
Negate
3 copies - 3 average
Essence Scatter
3 copies - 3 average
Doom Blade
3 copies - 3 average
Jace Beleren
3 copies - 3 average
Cruel Ultimatum
3 copies - 3 average
Sunken Ruins
2 copies - 2 average
Firespout
2 copies - 2 average
Haunting Echoes
2 copies - 2 average