1. The Look -
signature tooth gap, the plastic wristwatch, the late 80's Dad hat, buttoned up shirt, cuffed Levis. The goofy smiling, long tangled hair. Everything about the look is critical as an identifying factor. It's all constantly showcased in photos and video.
You can almost dress someone in this clothing for Halloween as "Mac Demarco." Similar approach for many other artists/musicians... i.e. Hendrix, Prince, John Lennon, Kurt Cobain, Bono, Slash, the list goes on...
2. The Songs, output and signature style -
Put out several releases in succession, all of similar quality, although the first release is a little rough around the edges. You can easily identify the sound as "sounds like Mac Demarco." His sound palette is consistent and includes: vibrato guitars, detuned synth, simplistic songs, laid back drums, mostly bass register vocals.
The trend since about 2010 seems to be the more releases you can string together in quick succession that all meet a quality standard, the more the Internet hype-beast crowds (and streaming platforms themselves) tend to award you with hype and credibility.
3. The Story -
The story about his absentee father, however real, falls into the "sob story" category we see all too often in the music biz come up game. The most often touted is the "I was dead broke, just trying to make it" type of story.
Along with the typical rags to riches overnight success type of narrative, he also seems to bolster his initial cult status, i.e. "underground hero" categorization with several myths that are most likely based on factual events. The most common include the myth of him sticking some of his phalanges into his anus whilst hanging from the ceiling at one of his shows, getting arrested at his own show, and being hammered drunk at many shows.
4. The Presentation -
If you want to look the part, you have to be the part. His Bandcamp page is full of not only the official releases, but all the demos, links to a seemingly never-ending set of music pages, his own wide array of merchandise (including ltd. edition figurines, and $60 plastic watches), his own webpage, a private fanclub, and a never-ending list of gigs and special presentations booked by a boutique label, each with a custom flyer. You find an overabundance of media, including countless music videos and interviews about his music and lifestyle. Anything you'd want to know is there in a variety of formats.
5. The Hype -
If you do a Google search you'll find hundreds of articles written in local to national-level media outlets. The classic photo-shoot and interview, sit-down interviews, collaborations with other artists, message-board threads, everything.
This is most likely 75% a by-product of everything, but I'm sure his PR team has a huge part in feeding the machine and keeping him extremely busy engaging with all the media outlets, his fans, and playing all the shows whilst also on a deadline to produce more music. It's a full-blown machine.
One last detail: The fact his music can be played at parties and social gatherings without anyone batting an eye certainly helps his "playlist" potential. The "chill vibe" helped him parlay his exposure in Pitchfork and other music review websites into a legitimate fanbase as well as a large portion of casual listeners and fans. If the music wasn't fun to listen to, he wouldn't be as big as he is.