Glys
Glys is a spren of an unknown type that formed a Nahel bond with Renarin Kholin.[1]
He grants Renarin the powers of the Truthwatchers, an order of the Knights Radiant[1] which gives Renarin access to the Surges of Illumination and Progression.[Falta cita] However, Renarin also has visions, which are also possible due to Glys' bond. This bond caused Renarin to hear screams when touching his killed Shardblade, which he initially believed to be a sign of his weakness or possibly insanity. Glys explained otherwise and told Renarin which order of Radiants he had joined.[1]
Speculation
Glys has not yet appeared in text, but it is possible that his appearance can be logically derived. If we make the assumption that spren of a given order appear the same, then we may have seen a spren like Glys. The shoemaker Ym had the ability to use the Surge Progression, his spren had the appearance of a glowing light, with tendrils reaching upward like a plant growing.[2] Both the Edgedancers and the Truthwatchers could use Progression, but we've seen the spren of the Edgedancers in Wyndle.[3] They take the shape of a growing vine with crystal specks embedded within it. So Ym is presumably a Truthwatcher, and thus Glys probably takes a similar shape to Ym's spren.