Spellsong

The Spellsong was the ability to invoke various magical effects through song and music, its practitioners were known as Spellsingers.

Effects
Spellsingers could use their arts to work a variety of magical effects, but the song of a single caster was not very powerful and could create magic whose power was comparable to cantrips or orisons. Multiple spellsingers could dance and sing in coordination to perform rituals capable of working more powerful magic, like healing wounded or ill creatures located near the casters (albeit generally not with the same power of major healing spells), sending simple messages, visions or indications to individuals known to the majority of the casters, repelling undead or evil creatures and making magic items glow, activate or levitate.

Particularly powerful spellsingers had the ability to use their song to call upon the Weave, invoking spells similar in power to those of a mid-level wizard or sorcerer.

Eilistraee's Spellsong
Priestesses of the goddess Eilistraee, especially Sword Dancers, were skilled in the art of the Spellsong and could use it to channel Eilistraee's magic to obtain effects of particular power. They had the ability to sing their magic even amidst the chaos of the battle, while dodging and dancing around or while wounded.

A single priestess could use the Spellsong to invoke magic equivalent to any 4th (or lower) level divine spell, or to return a single 4th (or lower) level spell cast through another Spellsong in the last two days to the mind of the priestess, to provide some healing to injured targets, or to grant spell immunity.

Multiple priestesses could join in a song and dance around a focus (which could be a creature to aid, a fire, a longsword with its blade planted in the ground or a holy symbol of Eilistraee), invoking magic of greater power.

The healing effect of the Spellsong was empowered when more than one caster took part in it; a group of seven or more priestesses could replicate the effects of the spells cure blindness, slow poison and cure disease; a choir of nine could dispel magic or remove curses and a group of twelve could even summon magic equivalent to the spell regenerate.