These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Arc Fatigue: The length of the Metroid Prime trilogy takes its toll on him. When he manages to get Proteus4994 to guest on a Corruption video, many of his comments are incredulous that slowbeef is still playing it.
Finding that Marc Laidlaw snuck in a reference to his pal Dave_o during a conversation the player has with the character Dave Forrest. Slowbeef had asked about it but figured there was nowhere it would fit in. It did have the side effect of Slowbeef forever thinking of Dave having Dave_o's voice.
Meeting and taking a photo with a Jonathan Ingram cosplayer at PAX. Especially Slowbeef's glee at finding that said cosplayer even had Jonathan's badge, cigarette and the photo of Jonathan and Lorraine (although he wasn't allowed to bring the gun.)
His special thanks to everyone in the thread and his especial thanks to Artemio Urbina for being the center of the Policenauts Translation Project to begin with.
His hope that Hideo Kojima will give a nod to, or at least know about said translation.
At one point Diabetus points out that they're getting the Grapple Beam awfully late, considering Samus started the game with it. "You've beaten Metroid Prime! Your prize: the Grapple Beam!" Compare this with the way Power Bombs are actually treated in Metroid: Other M.
Also, Other M's reveal that hearing Ridley's voice is enough to turn Zebesians, among other creatures, violent. Yeah, we can see why.
Another one is Slowbeef predicting that the Phazon suit will do a Venom-type thing and turn into an evil version of Samus that you have to fight. Guess what the Metroid Prime uses to turn itself into Dark Samus.
Diabetus has a rather uncanny ability to make jokey predictions that turn out at least partially true.
Near the end of the first Prime game, slowbeef, Diabetus, and Vicas make jokes about Samus getting malware. Come Sanctuary in Echoes, she does get malware.
While Diabetus is struggling with a boss in his Metroid Fusion LP (which was recorded during slowbeef's Metroid Prime LP) slowbeef smugly points out that he hasn't died three times to a boss yet. This is true until the Dark Aurora Unit which takes him six tries to kill.
Just Here For Ridley: After the Corruption LP was uploaded to YouTube, the most watched video by far is the Omega Ridley battle, with five times the hits of the videos immediately before and after it. There are also minor peaks for the Meta Ridley fight in the first game and the Amorbis fight in the second.
Memetic Badass: His portrayal of Shadow in the Dead to Rights games due to his ability to tear mooks apart and ability to do just about anything Jack tells him to.
Rescued from the Scrappy Heap: Arguably Toffile, who made his first Metroid Prime LP appearance as a straight man to Khad. His appearances in the Echoes LP were far better, as he served as a knowledgeable and effective guide while telling enough straight-faced lies to make "Toffile lied!" a Running Gag. However...
The Scrappy: Khad, according to slowbeef. He was unfortunate enough to make his debut in the Metroid Prime LP in a video that ran through a gamut of technical difficulties. In fact, around 80% of the video is composed of Khad complaining about his audio and slowbeef hurling insults at him.
Squick: As explained in supplemental parts of his Policenauts LP, he had this feeling when learning about how the player character could grope various women throughout the game, including Ed Brown's "young adult" daughter. It almost got to the point he considered quitting the project. Eventually it turned out it wasn't as bad as he feared and he decided to press on with programming the translation anyhow, feeling it wasn't his place to decide what players can and can't see.
Spoiled by the Format: The Omega Pirate battle in Metroid Prime begins with about eighteen minutes left into the video, and brings him and Samus close to death with a good eight minutes left. Omega Pirate dies two minutes later. The last six minutes are blank filler inserted just to subvert the trope.
Diabetus: You've created the most suspenseful Let's Play ever.
The Weird Al Effect: As discussed in one of ProtonJon's LPs, Slowbeef's Ridley voice is now known to some people unaware of where it comes from (an exaggerated version of Ricardo Irving's voice from Resident Evil 5). One likely cause is its frequent use in Retsupurae videos hosted on YouTube, while the Metroid LPs remained on less-traveled video hosting sites until 2013.