Mase led his squadron from the planetoid Annamar, hidden deep within a massive asteroid field near the Corellian Trade Spine.
He led several attacks on Imperial shipping, including the attack on a convoy that carried a piece of the Death Star II's weapons systems.
As Darth Vader decimated the Rebel base on Annamar, and dropped a BTL Y-wing starfighter on the starfighters stationed in the base, Mase and all the other Rebels were hit by the shockwave.
Mase was created by Tom Taylor for the story The Will of Darth Vader, which was the fourth volume of the Star Wars Adventures series of trade paperbacks. In the story, Mase was drawn by Brian Koschak.