The Blood Company
A quartet of semi-comatose elven mages
The Murmurers are four spellcasters, but they have no free will and are only semi conscious. Spellcasters can tap into their power and use them to cast very powerful spells.
Originally Kalash captured and enslaved them and Leech maintained them. After killing Kalash and sacking the Dark Tower, the Cohort claimed them. It is unclear if the Murmurers ever can be freed, but the Captain is not willing to just surrender this valuable military asset.
The Murmurers are a strategic magical asset; they have no responsive ability. It takes quite some time to employ the Murmurers so they are only useful when there is advance notice of the magical need.
Teach, Wander, Leech Spook and Fingers have all learned how to use the Murmurers. The Murmurers manipulate black and green mana, but working with other casters, they can tap into other mana sources.