Soul of Night

Soul of Night is a Hardmode crafting material dropped by most enemies killed in the Underground Corruption or Underground Crimson (in the Cavern layer), with a 1/5 (20%) / chance. This also includes enemies not native to the biome such as Granite Elementals.

Crafting all items, excluding the boss-summoning items and, requires 97 /   89 Souls of Night. One of each boss-summoning item and a Key of Night require an additional 24 / 14  Souls of Night.

Tips

 * An easy way to farm these is to go to the Underground Corruption/Crimson and summon King Slime using the Slime Crown. All of the Blue Slimes he summons have a chance to drop Souls of Night (this method will also work for the Soul of Light). * As of patch 1.4 slimes spawned in this manner will no longer drop souls of night or souls of light.

History
Seele der Nacht Âme de nuit Эссенция ночи 暗影之魂 Stickyrunneryt (hopefully)