Strange and wondrous creatures which spawn in magical biomes, these appear as a glowing orb flying through air and water. Each has a magical aspect, which is hinted at by their color. If killed, they will drop "ethereal essence", which bears not only the wisp's aspect, but also the precious aspect Aurum.
Wisps of "orderly" aspects are neutral, not attacking unless attacked, but those of "chaotic" aspects may attack unprovoked. Wisps attack with lightning from considerable range, but it doesn't do much damage, and Wisps do not pursue the player very well. Note that in magical biomes, wisps also spawn underground, where they are fairly well trapped and easily killed.
Wisps spawn in any magical biomes: Magical Forest, Eerie biomes, and Tainted Land. They are also common in the Nether. The rare Wisp Shrines (aka Obsidian Altars), are generally found atop mountains. Each contains a loot chest and a Wisp Spawner which produces only hostile Wisps. Converting these shrines to a wisp farm is fairly straightforward.