100% Completion: NCS didn't think he could get everything in Donkey Kong 64 because some of the golden bananas were extremely difficult for him to get, not to mention the Nintendo and Rareware coins, but he persevered and got everything. He was in complete shock.
A Date with Rosie Palms: Describes himself in part 5 of his Metroid LP as once having been able to do "it" with his thighs and not his hands, going to great lengths to avoid saying exactly what "it" is.
NCS: Right in your face, man, right in your armpit! How many different places on Bowser's beaten, battered, bruised, beleaguered, bludgeoned body can we hit next? (Beat) Those are all actually words, too.
Adorkable: Somewhat. He is a man in his 30's who enjoys video games and is generally a nice guy. The videos where he shows his face demonstrate how awkward he can be as well.
He also has done several in Final Fantasy IV, exactly where one would expect them. Cutting off before Rydia re-joins the party is one he claims he's wanted to do his whole life.
Creator In-Joke: "A BEEEEE!" It apparently came from an old home movie of his family's where he was freaking out over a bee.
Really, a lot of his catch phrases come from his old tapes.
Damn You, Muscle Memory: With all of the Zelda videos he's made introductions to, it's no surprise that he sometimes introduces a different game entirely as "The Legend of Zelda: [Game Title]" by accident.
Determinator: NCS is very skilled at some games, but he is capable of beating even those ones he isn't very good at, just because he NEVER. GIVES. UP.
Evil Laugh: He's not particularly evil, per se, but he does have a very distinctive laugh with which you'll become familiar after watching a few videos.
Failed a Spot Check: Multiple times in Yoshi's Story. Melons tend to get "camoflaged" in his fruit border, but one time he missed a melon right in the middle of the screen (and added an annotation pointing out his flagrant missage). In another episode, he spends several minutes in a panicked state, looking for eggs, without realizing that he has a full egg train following behind him.
Also happens quite often in his blind run of Conkers Bad Fur Day. He got a lot of flak one time for not immediately realizing he had to take cheese to a mouse.
In general, forgetting the obvious is quite common in his Let's Plays. His The Legend Of Zelda Twilight Princess LP features him buying a fire-resistant shield before entering the Goron Mines and then forgetting to equip it for the entirety of that dungeon. Amazingly, he manages not to lose his wooden shield despite nearly every room of that place containing fire and/or lava in abundance.
In the Starfruit minigame in Plants vs. Zombies, he continually fails to realize he has enough Sun to start planting them. He adds in annotations from the Starfruit, getting increasingly annoyed as NCS fails to plant him.
During his mostly-blind run of the final stage of the Lost World of Donkey Kong Country 2, after getting through a chunk of the stage, he wonders if there's a checkpoint. While it's right in the middle of the screen. Again. Cue more annotations. Another life later, he drops into the checkpoint STILL without noticing it, leaving him surprised to spawn there after he died once more.
In his blind run of DKC 3, during the run of the last world, he failed to note in Lightning Look-Out that the little lightning was the warning for the big lightning. He only noted this during a bonus game, 11 minutes into the video. During the same chapter, in Koindozer Klamber, he was desperately looking for a Bonus Barrel in the 2nd half of the level, and when he arrived to the screen of the Bonus Barrel, he kept throwing himself into the holes without noting the Bonus Barrel being just there. He just noted that like one minute later.
Also in his Mario Party 2 solo run, while he dominated the competition (See Crowning Moment of Awesome above), he forgot to show us the detailed stats for the Mystery Land board.
It's somewhat of a running gag in the DK64 LP, but an egregious example can be seen in Part 16. He ended a Bonus Stage with Diddy, but then, he leaves behind the Golden Banana without picking it up. As he put it out (a comment about that action in-video): "Umm... forget something?"
In the same LP (Part 43), in Crystal Caverns while he was getting a balloon for Tiny (which is in the same area as Diddy's blueprint), he got the balloon, but missed the obvious Tiny Pad, which leads to another Golden Banana. Approximately two minutes later, when he returns to the same area with Diddy to get the blueprint, he realizes he missed the pad while he was using Tiny, leading to having to return to the same place with her later on.
Again, during the DK64 LP (Part 67), when he was in Hideout Helm for the first time, there was a Pineapple Switch in plain sight (this switch allows you to progress further into the dungeon). He missed that switch various times. NCS changed his character from Lanky to Chunky... and he KEPT missing the switch, and he even got back to almost the beginning, being stumped. When he FINALLY found the switch, which was his excuse? The room was too dark to allow him seeing the switch.
Played with in the Conkers Bad Fur Day finale. Comments were saying it was okay to cry in the ending cutscene where Conker states he'd give up everything to have Berri back. He never did (if he did, he held it in), but did finish it off with a "You can't end the game like that!!"
"You can't hit me twice! You already got your turn! You already got your piece. You're like that kid who eats two pieces of pizza. Not that there's anything wrong with that, because there's probably two pizzas and five kids. So there's enough for each kid to have, like, two slices. Well, I don't have ten slices! I have sixteen, and you get four, so you actually ate eight slices! You know what, screw you. Maybe you should go to the gym."
A mild example, but he also has a tendency to randomly sing a few lines of a song in some episodes of his LPs.
My Greatest Failure: A relatively lighthearted example, but he'll never forget the "I'll take Tyson" incident from his childhood. He's even mentioned that he cringes whenever his sister brings the sentence up.
A much smaller example was when he realized he slipped off the bridge in Gerudo Valley and left Epona up there.
"Goodbye, my horsey. Goodbye!"
In one of his Plants vs. Zombies videos, he was feeling very happy because the game's composer (the one responsible for the "There's A Zombie On Your Lawn" song) found one of his videos and liked it. He was happy for a few minutes before he realized she'd heard him singing his gross toilet-based lyrics over her awesome music. His mood flipped around rather quickly.
Old Shame: His Final Fantasy VI let's play, which was done via camcorder. He's expressed dislike at how bad he was at LPs back then and has expressed the desire to re-do it at some point.
Painting the Medium: When text boxes in games have proper nouns in different colours, he sometimes says "COJIRO!" as a Call Back to a joke he did based on this in Ocarina of Time.
Calling Bowser a float in Super Mario Galaxy 2. Lampshaded the second time he does so, asking "Will this be the running gag for this LP?" No, it wasn't. In the final battle, there was no mention of floats.
Too Kinky to Torture / Wasn't That Fun?: He'd only ever played the first couple of levels of Battletoads before taking part in the first four-player race. His reaction to the later levels of this notoriously Nintendo Hard game? Saying how fun it was and how he wished he'd played it growing up, to horrified reactions from the others.
The Unintelligible: His take on Professor Owlan in Skyward Sword has him speak in very fast gibberish.