Mandrakk

"Look at them all, all those lives you could lead. Do it, John. Do it. Drink of The Bleed Mandrakk hid within the cube. Feel its power. Break through the Source Wall, for when you break through that wall, all those worlds that await will be yours."

- Eobard Thawne to John Diggle

Mandrakk is a cosmic entity who hid part of The Bleed within a cube containing a Green Lantern Power Ring.

The Bleed
At some point, Mandrakk hid part of The Bleed within a cube containing a Green Lantern Power Ring.