[7] After college, Mustard joined computer graphics studio GlyphX along with his brother Geremy, where he created video game cutscenes for publishers such as Eidos Interactive, Activision and Sony.
[7] In May 2005, just prior to the release of the game, Mustard left GlyphX and founded Chair Entertainment along with his brother and Ryan Holmes, and hired several of the developers of Advent Rising.
[8][9] At the "Apple Special Event" in September 2010, he joined Steve Jobs on stage to demonstrate Infinity Blade (then known as "Project Sword"), which was released two months later.
[8][9] Mustard, who was the creative director for that version of the Fortnite and "Loremaster" for the overall project,[13][9] incorporated characters from media franchises, including Star Wars and Marvel.
[3][13][16] Mustard had met filmmaker and AGBO co-founder Joe Russo in 2018, when they had collaborated on bringing Marvel villain Thanos to Fortnite and later became good friends.