Willowisp

Probably the most annoying and perhaps dangerous creature in the game if you are caught off-guard. These things cast Lightning that always rolls high damage it seems. To make it worse these things can target and kill you from off screen. Be wary crossing the

Great Marsh and Worldstone Keep, gangs of these spirits have been known to strike characters dead in an instant. Beware the strongest variants... Black Souls. Any character with low health or low resistances are especially susceptible to instant death from these powerful lightning casters. Only plus side, they are extremely fragile and easy to kill.

Ghost Busting (Hunting) Guide Touching on Fundamentals & Areas to Focus on

Ghosts (

Wraith,

Willowisp and

Finger Mage) have a higher chance to drop runes as other normal monsters in D2.

These already dangerous monsters are immune to freezing and Chill effects in Hell difficulty, making them even harder to pin down and engage.

From the

Arreat Summit:

Willowisp use a Lightning attack, so equipping Lightning Resistance gear will help against them.

Willowisp are almost invisible until they attack. You might be able to see traces of them as they move. They can be attacked while you cannot see them so lay down some area effect spells if possible.

Willowisp attacks drain Mana.

They appear also in

Worldstone Keep Level 2,

Throne of Destruction

Frozen River.