Tib and Rob are two brothers who are trained by their mother every day, being repeatedly told they're the heroes of the legend who are destined to save the world. They soon get bored with life on their small island, and make a promise to escape together one day.
Years later, when wondering if they are ever going to escape the island, their world suddenly start glitching out. With their mother gone, only having left behind a letter and a strange controller, they are asked to meet her at the communication tower, and after summoning a portal orb leading to a space station with similar portals to other worlds, their adventure through a variety of retro-game inspired worlds to save said other worlds from the glitches start...
Old School Musical provides examples of the following tropes:
- Abusive Parents: In the first chapter, a drawing by the then three-year old Rob portrays Big Mama as standing over Tib and Rob with a whip in her hand, and Tib comments that it's rather realistic, though he forgot to add spikes to the whip. She put them through Training from Hell from an early age to the point where Rob's 16th birthday wish is one day without training, and once locked Rob outside of the house for three weeks in the middle of winter when he was a kid. Though as it turns out, she's not actually their mother, but rather the Big Bad who raised them only to help them further her evil plan...
- All Bikers are Hells Angels: The tough-looking, leather vest-clad Robertosan and his biker gang, who start chasing you after you drive away from the contest.
- Big Guy, Little Guy: Tib and Rob are short and tall, respectively.
- Big Little Brother: Rob is much taller than his 7-years-older big brother Tib - the first chapter shows this has been the case since he was three and Tib was ten.
- Developer's Room: The village features a house labeled "La Moutarde" where you can meet the devs.
- Evil Matriarch: Big Mama isn't only abusive towards Tib and Rob, but turns out to be the Big Bad of the game who set them up from the start to help her spread the glitches around the universe. She's not their actual mother, though, and Tib and Rob don't see her as this anymore when her true identity is revealed.
- Expecting Someone Taller: When Tib and Rob are looking for the great sage Cloche-Pied, they meet a strange green creature only to find out, to their surprise and slight disappointment, that he's said great sage. When being asked if they were expecting an old man with a beard, Rob admits yes.
- Hand Wave: When Tib and Rob ask their mother why she couldn't bring the virus-spreading letter with her herself, an error message saying "The script has encountered an error and needs to be updated: Please wait..." shows up and it's explained that only they could bring it with them without getting infected because they're the heroes.
- Height Angst: Tib is sensitive about his short height, and gets annoyed whenever someone refers to him as short.
- I Am Not Your Father: The final level reveals that Big Mama is not Tib and Rob's mother after all, but rather "Xelivad, Ruler of Glitches, the Shadow of Arckhania", the Big Bad behind all the glitches, who destroyed Arckhania, killed their parents along with other survivors, and raised Tib and Rob to help her take over the universe.
- Ice-Cream Koan: Cloche-Pied will sometimes say nonsensical sayings like "the morning star eats a carrot, but the rabbit doesn't." Tib and Rob point out how they don't make any sense.
- Interface Screw: While many of the levels feature glitchy effects, the final level is where they start affecting the interface and UI, making it glitchy and choppy.
- The Chicken Republic post-game mode uses this for all levels, often with more than one effect on a level, including but not limited to having the notes change in size, occasionally zooming in towards the middle of the screen, warping the middle of the screen, making the visuals more pixellated or having chickens fall down across the screen.
- A Minor Kidroduction: The first episode takes place during Tib and Rob's childhood, with them being ten and three respectively. At the end, it skips forwards to 13 years later, from where the rest of the game happens.
- Ocular Gushers: The announcer of the Beach City Clash competition has waterfalls of tears streaming down his face after getting insulted by Robertosan.
- Ominous Visual Glitch: The game's plot is based around glitches corrupting various worlds, and the levels and cutscenes frequently show glitchy effects.
- Retraux: The game is drawn in a pixel-art style, has a chiptune soundtrack, and features parodies of many retro games.
- Small Town Boredom: Tib and Rob are sick of life on their small island, and wish to one day escape from it and see the world beyond the island. One day, they get their wish... as the world start glitching out and they escape from it, starting their adventure as they start exploring other worlds.
- Sweat Drop: Tib occasionally has a small sweatdrop appear above his head in cutscenes, as a reaction to stupid comments, unexpected problems, and similar.
- Training from Hell: Big Mama put Tib and Rob through tough training from their early childhoods, to train them into becoming heroes, although it's later revealed it's all part of her plot to help her further her plan to take over the world. From what we see and hear, it involves, among other things, throwing various objects at them and making them do huge amounts of push-ups.
- Unwitting Pawn: The note from their mother Tib and Rob brought with them? Actually the cause of all the glitches happening in the other worlds they visit - which was her intention all along, as this would spread a virus across the other worlds, letting the heart of the internet be infected and spread corruption through the other universes.
- Volleying Insults: The Beach City Clash Competition in the Outrash stage is a contest based around this, with the competitors throwing insults at each other and trying to make the other person cry. Tib and Rob get dropped right into a match and join for a short while before driving off.
- Who Writes This Crap?!: After it's explained to Tib and Rob that they are the only ones that could carry the glitch-spreading letter with them without getting infected themselves because they are the heroes of legend:Tib: That's the worst explanation I've ever heard.Rob: Maybe the writers are on strike?
- Your Mom: One of Robertosan's insults to Tib and Rob in the Beach City Clash Competition is "Yo mama's so fat she looks like the Neon City Tower". Tib takes this to mean their mother is in Neon City and starts driving there.
