Cargill wrote for Ain't it Cool News for nearly 10 years under the pseudonym Massawyrm, as well as serving as a staff writer for Film.com and Hollywood.com. He appears as the animated character Carlyle on spill.com, where he also hosts a featured podcast. His first screenplay, the critically acclaimed SINISTER, was co-written and directed by Scott Derrickson and starred Ethan Hawke. He co-wrote the screenplay for Marvel's DOCTOR STRANGE.