Wisps appear as floating balls of energy in the air, their colors varied by their aspects.
They normally fly in large sweeping arcs, passing freely through water and perhaps some transparent blocks. However, if found underground or indoors, they are essentially trapped. Each wisp has an aspect, which determines its color and whether it is initially hostile to the player. (Otherwise the aspect seems not to affect their abilities.) Some aspects (especially those based on Perdito) will attack unprovoked, while others will attack only if the player attacks, or possibly if the player stays nearby too long.
Their attack is a narrow beam of electricity, not very accurate and with low damage -- but they can use it repeatedly while floating above you. They are somewhat evasive, and even with a bow hitting them can be difficult. However, they are not very persistent: If the player just runs away or takes shelter, the wisp is unlikely to follow, and may just wander away. If actually hunting wisps, a Thaumostatic Harness is helpful, and a shock focus is the preferred weapon. Golems have an even worse time with them: Even with a dart launcher, they don't use it, instead hopelessly trying to melee the out-of-reach wisp.
Wisp spawners are found in obsidian-tile "wisp shrines", generally found atop mountains, which also offer a loot chest and a sinister node. The wisps from these spawners will be from a short list of hostile aspects. The spawner can easily be converted to a golem-run wisp farm:
- Replace the shrine structure with the usual 8x8x3 or 9x9x3 mob farm room, centered on the spawner. Fence off and light the top, to prevent the sinister node up there from spawning Furious Zombies. Provide a route up there if needed -- this will be a good place to hang out overnight.
- At this point, you basically have a manual farm -- you can just close it up except for a door or two and some firing holes.
- Otherwise, fill the spawner layer with dirt, leaving a couple of "golem staircases" between the levels.
- Set up an entrance hall to one side, with a gather golem attached to a chest you can reach from outside.
- Place two guard golems, Stone or better, with fez, mace, and visor, and perhaps some upgrades. Due to the two 1-high floors, the golems will be able to reach and attack any wisp in the farm, many of which will be trapped in the dirt anyway.
- Optionally, place a couple of Brain-in-a-Jars on either side of the dirt layer, accessible from the outside or the entrance.
- Since wisp farms are usually on mountaintops, you have a lot of space beneath (in the Eerie Zone) for building, should you wish to construct a mana bean farm.
Drops ethereal essences that will contain 2 Auram and 2 of the wisps' aspect. As such, an ethereal essence of Auram will have 4 Auram and an ethereal essence of Terra will have 2 Auram and 2 Terra, and so on.