Masha was a shapeshifting child of the Mockinglord, embodying chaos. She took possession of Maurielle Jahimis ten years before the Eclipse in which she would play a major part.
Her most daring act before the siege of Falor by the Faloran Republic was to coordinate an assault on Wisefire's home ground, the Crucible, to steal forbidden and critical lore. The attack succeeded, and the secret to killing the Arbiter was given to the Godslayers, who then succeeded in doing so.
Similarly, Masha managed to smuggle the runes for Binding Radiance out amongst many other terrifying things - and this knowledge was traded to the Inquisition of the Republic. Masha intended to kill Radiance during the Eclipse, having allied with Black Sun, and mortally wounded High Palatine Manlia Suren Issander and also the Seraph Lightdancer, before she was cast out of Maurielle Jahimis by the Silhouette of Stars when tampering with a spirit well.