Cursed Flame

The Cursed Flame is a Hardmode crafting material. Its Crimson counterpart is Ichor. It is found by killing World Feeders and Clingers, both of which can be found in the Underground Corruption.

While important as a crafting material for the Cursed Flames (magic weapon), Cursed Flame can also be used for making Cursed Torches, Cursed Arrows, and Cursed Bullets. Since these are all consumable items, having a steady supply is important for exploring caves and using many ranged ammo-based weapons.

Trivia
The cursed flames may be a reference to the Wild Fire from the Battle at Blackwater Bay, Game of Thrones