Accidentally Accurate: Max jokes near the beginning of Digital: A Love Story that the people he talks to can't be human, because they're too polite to be a human being on the Internet. As it turns out, most of the people he was referring to are actually AIs and not real people.
Colbert Bump: His appearance in ERBParodies brought himself a moderate influx of attention. Worked the other way too, with ERBParodies becoming substantially more popular after he joined.
Peter tells a story of how this happened to him; he donated a copy of Don't Starve to another let's player, who gave shout outs to Peter at various points throughout his playing of it, leading to this taking effect.
Development Hell: Thousand-Year Door went on hiatus a while ago, and Max has finished three fillers for it without any sign of continuing. He appears to have cancelled it, judging by what he said in MLP RPG.
This was what eventually contributed to the temporary cancellation of Classification: Awesome.
Plenty of his LPs have gone on hiatus at some point. Nowadays, since he doesn't schedule the uploads of specific LPs, this only comes into play when something goes on an official hiatus, such as Halo 4.
Doing It for the Art: He doesn't do any of his stuff for money, and he doesn't stop doing it just because some people don't like it. He only stops if he himself doesn't like it. Even after he partnered with Maker Studios, his quality has stayed the same.
The Batman voice (or "demonic voice") also counts as this. It hurts him greatly to do it, due to harming his throat and making him lightheaded (and even sick at one point), but the keeps it up because it's entertaining.
Fan Community Nicknames: He calls people who watch his videos "the viewers". He also uses that name for people who listen to his music or read his fanfics, even though there's not really any "viewing" involved with those two. This actually came about due to Insistent Terminology, as he refused to call them "fans" for fear of sounding egotistical by saying things like "I have many fans".
Fake Brit: Zero is American, but is portraying the Doctor in Doctor Whooves: Chaotic Companionship.
Harpo Does Something Funny: While parts of Classification: Awesome were scripted, Max made up a lot of what he said as he was saying it. If he said something he felt was good, but the recording had to be scrapped, he jotted down what he said so he could use it again.
He Also Did: There are very few people who watch Max's YouTube videos and are also aware that he writes My Little Pony: Friendship Is Magic fan fiction as well. Works the other way too, as few people who read his stories are aware that he does YouTube videos.
Let's PlayingAgainst Type: He's usually known for comedy coming from screwing up puzzles, battles, or plans. When he plays a visual novel, he can't do much aside from read everything and snark about it.
Lying Creator: Max claimed at the end of Wii Party that Paper Mario: The Thousand-Year Door would resume next week...instead, next week has no upload whatsoever, and the week after he begins a new filler Let's Play instead, this one for Portal 2 with newcomer Jacob / Nameless Warning. And a while later, the LP was cancelled entirely.
Old Shame: His Ocarina of Time let's play; he really doesn't like it.
It reached the point where it became Playing Against Type for him when he didn't play a creepy character and instead played Phoenix Wright.
Schedule Slip: Frequent early on, but has decreased lately. Super Vexation Saga still suffers greatly from this due to optimal times for recording being few and far between, and The Drawing Board episodes are occasionally delayed a day or two, but for the most part, this has stopped taking effect.
Throw It In: Max often puts little clips at beginning of episodes before his intro. Usually these clips are of things that happened before the recording officially started, such as conversations.
Un-Canceled: Max has a habit of stopping work on Classification: Awesome, then starting it up again several months later as a "new season".
What Could Have Been: Battletoads was going to resume with Marioman2233 still co-commentating, but due to Max losing contact with him for unknown reasons, Zero joined instead.
When playing The Walls, they were apparently planning to have a free-for-all at one point, but ran out of time.
Before creating Challenge Foolishly Accepted, Max had planned a short series titled "Wiisomnia", where he would play three Wii Play games every day for three days, not sleeping during the nights in between, to see how his playstyle changed. When he lost the recording of the first day, he just scrapped the idea. He later came back and played all nine games for Challenge Foolishly Accepted, but with only one night of no sleep.
Before its cancellation, Classification: Awesome was going to have a review of (presumably) Kirby's Return to Dream Land. The review was later done to start off season 3 when the series was brought back.
Plenty of projects were planned, but never went anywhere. Some even got to the point of being officially put on Max's update schedule.