The entirety of Thank You, A new year and 50000 Subscriber Special, where Mark shows just how much he's happy about what he does, and how happy he is to have his audience, and how thankful he is for all of them to help him get where he is now.
All of his "thank you" videos are very heartfelt, particularly his 1000th video special. In "Draw My Life," Mark really goes in-depth into his pre-YouTube home life and his motivation for making videos.
His video when he reached one million subscribers is very low-key, showing a montage of some of his best moments while he talks in a very low tone about how much the channel and his fans mean to him.
During his Dead Space 3 walkthrough, when who enters a bunker, he encounters Buckell who, moments later, dies from hypothermia. He expresses that he liked the character and is quite sad that he had to die. Whilst he isn't really devastated, its nice to know that Mark at least shows that he has some care for the guy. Especially when he exits the bunker, he states that he will not even try to stomp Buckells body, even though he greatly distrusts dead (or supposedly dead) bodies.
The entirety of Mark's "Farewell Charity Livestream" promotional video, put out three weeks in advance as a send off to his time spent in Ohio before moving to LA. He spends the entire video gushing about how much he loves his work and thanking the fans for supporting him since the channel's inception, and for donating to the cause of each livestream. You can just hear how much this means to him in his voice as he talks about how much he appreciates the support of his fans, and it tugs on your heartstrings to hear that, especially how much time he puts forth towards each and every video he makes. Even though he says he "feels like an old man in a younger man's body," his enthusiasm for what he does is just palpable, and it really speaks to him as a person, as well as an entertainer and gamer.
The last part of his playthrough of Outlast: Whistleblower is simply full of Mark having multiple fanboy moments over the various nods to continuity. The way he gushes is pretty nice to see.