Justin has acted in five episodes. In the Spider-Man episode he played the title character. In the Fester's Quest episode, he plays Cousin Itt whilst composing a parody version of the Addams Family theme song. Since the Battletoads episode, Justin was given his own persona as the Angry Video Game Nerd's "Guitar Guy" who lives behind his couch, and plays and sings his theme song.
In the Bugs Bunny's Crazy Castle episode, Bugs Bunny destroys the Nerd's couch, leaving the Guitar Guy to assist the Nerd in facing Bugs. In the Ikari Warriors episode, the Guitar Guy had died because the Nerd had forgotten to feed him.
When the Nerd needed someone to play Ikari Warriors with him, he found the Guitar Guy's skeleton behind his couch, holding a guitar and wearing a hat. With an NES controller, the Nerd used the resurrection cheat code from the game and brought the Guitar Guy back to life to ask for his help in beating Ikari Warriors. Justin improvises a whole song in this episode titled: "Where Did Their Hair Go?"
Kyle Justin is also a musician, and some of his non-Nerd songs have been recorded on YouTube by Cinemassacre. He took a hiatus from AVGN to devote himself full-time as a husband and father in 2009.
Since then, Kyle has helped out behind-the-scenes in some of the AVGN episodes, being credited for the creation of the set used in the Sega Activator Interactor Menace episode, the fake wall used in the MEGA MAN Games episode and the 13 Dead End Drive set used in the Board James episode Nightmare.
Angry Video Game Nerd Adventures
The guitarist later appears as a playable character in Angry Video Game Nerd Adventures. He is simply a living skeleton, donning his brown trilby and wielding his iconic guitar that shoots waves of deadly energy and can pierce through walls. He is found in the stage Future Fuckballs 2010 where he is sucked into Game Land along with the AVGN and his other friends.
His skeleton appears in the Schwarzenegger Games episode along with his guitar , and the skeleton is seen standing up in the Dark Castle episode.  Justin also appeared in TGWTG Team Brawl, assisting the Nerd. He also made a parody version of the Nerd's theme for the Nostalgia Critic's review of Bebe's Kids for the SNES.