Hearthstone is a trinket in Fiend Folio, a mod for The Binding of Isaac.

Using a card activates a random positive effect from the following:
• The Necronomicon
• Heals 1.5 Red Heart containers.
• Spawns 4 Hollow Friends that last for 1 room.
• Anarchist Cookbook
• The Book of Sin (3x uses)
• Uses 3 random pills.
• Butter Bean
• Book of Shadows

The following special synergies and interactions for Hearthstone have been documented.

* Note that not all possible synergies and interactions are listed here.

• Check out the trinket description on the mod's external Wiki.
• Download Fiend Folio from the Steam Workshop.