XI - Strength?

How do you unlock XI - Strength??

In The Binding of Isaac, XI - Strength? is unlocked by earning the Ultra Greedier completion mark as Tainted Samson on hard mode.

All enemies in the room are weakened, becoming slightly slower and taking double damage from all sources. Affected enemies also have their damage reduced to half a heart. The effect lasts up to one minute, or until the room is left.