Faerie fire

Faerie fire was a evocation or alteration spell that outlined a target.

Effect
Faerie fire caused a glowing lining around targets in a selected area. In most versions, the spellcaster could chose the color of the glow, picking between green, blue, violet, or red.

All versions of the spell made a target easier to hit,  but the post-Spellplague version also caused radiant damage and slowed the target. The pre-Spellplague version negated the effects of spells like blur or darkness.

Components
Other than the usual vocal and somatic components  one version needed foxfire.

Users
Drow had the innate ability to cast faerie fire. This ability was granted to them by Faerzress. The drow used the ability in combat as well as to decorate their cities.

Experienced knights of the Blue Moon gained the ability to cast faerie fire up to three times per day.