Vade Retro

How do you unlock Vade Retro?

In The Binding of Isaac, Vade Retro is unlocked by earning the Ultra Greedier completion mark as Bethany (Character) on hard mode.

While held, enemies leave behind ghosts on death. Stronger enemies leave bigger ghosts. Using the item causes the ghosts to explode and damage nearby enemies, and instantly kills all ghost enemies with less than 50% HP.