The end of the Final Fantasy theme dials back the "epic" and dials up the nostalgia for those summer vacations from our childhoods, that we spent "dancing in our jammies 'CAUSE WE BEAT FINAL FANTASY!"
Mario Paint which is entirely about how much he loves the game and how it inspired him.
Brent has this big warm smile on his face throughout the video. He's clearly happy to be singing about Mario Paint.
To a lesser extent, the Civilization song. Though there's no shortage of jokes in it, it's pretty clear that Brent truly loves the game, and the song is focused more on singing its praises than making fun of its premise.
"Baby Mario & Papa Yoshi". The song is about how Yoshi initially wanted to eat Baby Mario but then decided not to and instead raise him into the hero he is today. When you see them spending time together during the Good Times Montage in the music video, it's clear that Yoshi really does care for the little guy.
To put this into perspective, a song about eating babies and poopy diapers was made into something completely heartwarming.
Also the fact, the heartwarming montage takes up half the song, where in that space could have been easily used for more silly lyrics. This is even lampshaded by Brent
brentalfloss: The biggest reaction I got was "adorable" that's a new one.
It's still heartwarming even when you notice the Funny Background Event of the Yoshis making stew. Look closely at the ingredients...
From his first CD, "What If This CD... Had Lyrics?" (both versions, the normal one and the G-Rated one), there is a song called "Corey" where he sings a little ode to a girl on Screwattack he likes. The G-Rated version is even sweeter in my opinion, for instead of talking about getting "into Corey's Corner", he talks about how he plans to propose.
Honoring the DuckTales game remake, "Just One Duck" revolves around how determined Scrooge is to go on adventures and find money, and how inspiring these adventures are. Many Intenet personalities like Spoony, Uncle Yo, Team Four Star, and The Nostalgia Critic join in and raise signs thanking or praising Scrooge. At one point early on, you can even see two kids, (a boy dressed like Megaman and a girl dressed like Roll) one of them holding a Wii U gamepad with Ducktales on and the other holding a sign saying "Yay, Ducktales!". Everyone has this huge smile on their face, you can tell they're happy to participate.
'Cause just one duck can win the day
Other stories pale to the Ducktales you've lived through
One duck answered every call, became an uncle to us all
And Uncle Scrooge, that crazy duck is you...
Listen to me, Uncle Scrooge, 'said we love you
Zidane to Vivi, which is about Zidane telling Vivi not to let the bad things in his life get him down and enjoy childhood.
His song announcing the end of the Brentalfloss comic strip is full of warm fuzzy nostalgia, and is not only a grand farewell to the comic, but also to the original characters in the comic that the fans grew to love. Not to mention the amount of feeling he puts into it, it sounds as if he's singing an farewell to his own child.