Spirit Stone

"As light as a feather, and you can almost see through it. Some people say looking at it for too long can change your personality."

The Spirit Stone is a Reforge Stone that applies the Spiritual reforge on any Bow. It can be found on The Catacombs - Floor IV.

Dungeon Reward Chests
The Spirit Stone has a chance to drop from Diamond, Emerald, and Obsidian Dungeon Reward Chests on The Catacombs - Floor IV.

Thorn
The Spirit Stone can be obtained from, after killing Thorn 50 times.

Trivia

 * It is currently considered the best reforge on bows in dungeons.