Creator Backlash / Old Shame: Joel has openly spoke out against his work with MELLEEFRESH between 2007 and 2008. He detests the vapid lyrics about being the biggest whore you possibly can, which have rendered them unlistenable to him. (Song names include "Sex Slave", "Attention Whore" and "Something Inside Me".)
Raise Your Weapon is minor one for him now, due to him basically admitting he made a Dubstep song to sellout, and that he pretty much hates Dubstep now. This may or may not have to do with his falling out with Skrillex, though.
Development Hell: "United We Fail", his upcoming graphic novel project, is currently in this, if not outright on hold at the moment. He cited Executive Meddling "making it not fun" as why.
Executive Meddling: "Ghosts 'n' Stuff" was originally titled "Ghosts 'n' Shit", but his higher-ups wouldn't let him release the song with that title.
United We Fail was put on hold in part because of this trope: he was sick of the suits and businesspeople getting involved in the project and making it "not fun".
Fan Nickname: "Deer Bus" for "Professional Griefers". Before the official title was revealed, the fandom gave the song that name after someone mentioned that the hard-hitting bassline sounded like "a deer getting hit by a bus".
"Professional Griefers" also has the nickname "Into the Nether" among Minecraft fans, thanks to the song's association with MineCon in that fandom.
Keep Circulating the Tapes: There are several songs that are on his SoundCloud and MySpace accounts that haven't been officially released or even available for download. These not only include rather...odd songs, but earlier versions of existing songs (such as "Old Ghosts" - see What Could Have Been below), remixes of existing songs, and live edits.
All of his early work, especially since Section Z, the music site that hosted it, is now gone. Project 56, deadmau5 Circa 1998-2002 and A Little Oblique are compilations featuring much of his early work. Many one-off tracks are circulating around the internet as well, such as "asdfghjkl", "Limit Break" and "Brazil".
"October" reached memetic status in this regard, originally appearing in a handful of live shows in 2008. It finally saw release on > album title goes here <, in 2012.
He also has a replica Master Sword and Hylian Shield, and is now collecting video game weapon props, one of which being the chainsaw from Lollipop Chainsaw. Also has a Creeper hat, several Minecraft t-shirts that he occasionally wears, and two replica Creepers in his living room.
His love for Minecraft is so legendary that he performed at MineCon for free and is friends with Notch, the game's creator. And as previously mentioned in The Cameo, he has his own line in the game's main menu splash. He also runs his own multiplayer server, mau5ville.
He's also quoted and mentioned Final Fantasy X many times on Twitter. "Yuna may pass.... Guardians may pass..... SOFI NOT PASS!!"
He explictly stated in the Valentine's Day 2012 stream that he is, indeed, a Vocaloid fan.
As a whole, he doesn't just fulfill the "major nerd" part of this trope, but the literal meaning of it, being a pretty normal guy who is close to his fans. He watches his Twitter like a hawk, answers questions, reads and keeps all of his fanmail, does livestreams in his home, and makes silly videos (some of which involve his beloved cat). Several comments on YouTube reprints of his livestreams are along the lines of "he seems more like a friend than a celeb".
Schedule Slip: His new studio and house renovation was originally supposed to be done in December 2011. The end-date for the studio was moved to February 2012, and then again to March 2012. Consequently, the official release of "Professional Griefers" and the album, > album title goes here <, have also been pushed back.
As seen in Executive Meddling above, "Maths" was originally supposed to be released mid-January 2012, before finally coming out mid-February 2012.
"Aural Psynapse" is actually a re-edit of a song that he made in 2001 under his old Halcyon441 name, also titled "Aural Psynapse". Not only are the synth lines similar, but the background effects used in the song (which are especially obvious right at the beginning) later showed up in "Strobe" and "HR8938 Cephei".
Speaking of "Strobe", the song is actually two previously existing songs put together, one of which being "Then We Stood Still".
Like "Strobe", "Fn Pig" combines "Get in the Cart, Pig" with what ended up being an entirely different song. Several uploads on his soundcloud show him toying with different ways of continuing the massive "Cart" introduction, with the original upload ending in what sounds like a 90s rave.
"Brazil" was originally much more chill and meditative. It's completely unrecognizable from "Brazil (2nd Edit)."
It was mentioned in a livestream that he had actually received several vocal submissions for "Maths", but decided to keep the song as an instrumental.
He said on the Joe Rogen podcast that he was one of the artists considered for doing the soundtrack to TRON: Legacy before Daft Punk was chosen, and added that had he been chosen and he knew that Daft Punk was being considered, he would've handed it off to them anyway.