20 feet. Urkhas is itself naturally invisible, but glows with a violet light, casting bright light in the aura and making it visible.

Glow

Urkhas is immune to all spells except <a href="/spell/faerie-fire">Faerie Fire</a>, <a href="/spell/revealing-light">Revealing Light</a>, <a href="/spell/force-barrage">Force Barrage</a>, <a href="/spell/quandary">Quandary</a>, and spells with the good trait.

Magic Immunity

Requirements An enemy is being affected by a fear effect or <a href="/condition/dying">Dying</a> within 15 feet of the will-o&#x27;-wisp.<hr/>Effect Urkhas feeds on the creature&#x27;s terror. It regains 1d4 Hit Points, and if it has Gone Dark, its glow reignites.
Urkhas can take this action only once per round.

Feed on Fear

Urkhas extinguishes its glow, becoming <a href="/condition/invisible">Invisible</a>. It can end this effect with another use of this action. If it uses its shock attack while invisible, the arc of electricity lets any observer determine its location, making the Urkhas only <a href="/condition/hidden">Hidden</a> to all observers until it moves.

Go Dark

Urkhas (3-4) - aberration, air, evil, fiend, unholy

Urkhas is immune to all spells except @UUID[Compendium.pf2e.spells-srd.Item.Faerie Fire], @UUID[Compendium.pf2e.spells-srd.Item.Revealing Light], @UUID[Compendium.pf2e.spells-srd.Item.Force Barrage], @UUID[Compendium.pf2e.spells-srd.Item.Quandary], and spells with the good trait.

Requirements An enemy is being affected by a fear effect or @UUID[Compendium.pf2e.conditionitems.Item.Dying] within 15 feet of the will-o'-wisp.<hr />Effect Urkhas feeds on the creature's terror. It regains @Damage[1d4[healing]] Hit Points, and if it has Gone Dark, its glow reignites.
Urkhas can take this action only once per round.

Urkhas extinguishes its glow, becoming @UUID[Compendium.pf2e.conditionitems.Item.Invisible]. It can end this effect with another use of this action. If it uses its shock attack while invisible, the arc of electricity lets any observer determine its location, making the Urkhas only @UUID[Compendium.pf2e.conditionitems.Item.Hidden] to all observers until it moves.