Soul of Sight

The Soul of Sight is a crafting material that drops from The Twins. The Soul of Sight is essential for making most Hallowed magic weapons, including Magical Harp, Fairy Bell, and Rainbow Rod. It's one of the three souls that is dropped from the Hardmode bosses, others are the Soul of Might, dropped by The Destroyer and the Soul of Fright, which you can get for killing Skeletron Prime.