Demonite Bar

Used to create unholy weapons, or together with Shadow Scales to make nightmare tools or Shadow Armor.

Demonite Bars are smelted from Demonite Ore, which is dropped by the Eye of Cthulhu, Eater of Worlds, and, as of 1.0.5, can be mined.

Demonite Bars have moderately high value, so selling excess bars for profit may be a good idea. Note that selling raw demonite ore will yield the same payoff.