SoulKey
Discover the Soul Key trinket, an all-new addition directly from the Genesis+ mod!
The trinket makes it so that whenever you use a key, you have a chance of spawning a soul heart. Not only that, but when you find yourself out of keys, holding the key will make you use a soul heart to open doors and chests instead! Beware though, as the key only wants those who are pure of heart, and will not work if the player has some black hearts.
The trinket will spawn in naturally in the game, with a chance of 1 in 300.
Be sure to check out The Binding of Isaac: Genesis+ mod at http://steamcommunity.com/sharedfiles/filedetails/?id=839571644
