Of Slap City's 11 character roster and the 6 (technically 7, including PsyCard) game series represented within it, only Ittle Dew and Princess Remedy are the main protagonists of their respective source material.

If one is to scan the QR codes summoned by Business Casual Man in his neutral special, they can take you to one of 4 websites including:

• A fake business document.
• An alignment chart of fake band names.
• A You're The Man Now Dog-style site with looping GIFs of Business Casual Man.
• A text adventure game starring Business Casual Man.

If Business Casual Man saves up his money to the maximum amount ($1000) and then uses his air strong, he will summon the trail of bouncing cards from Windows Solitaire as a one-hit-kill projectile.

The layout of the Traffic Jam stage in Nickelodeon All-Star Brawl, consisting of a bus driving along moving asphalt that players can fall onto and either ram into the bus or get conveyed off-screen, while cars appear to the left and right to stand on, is recycled from a stage from Ludosity's first platform fighter Slap City called Public Transit, with the main difference aside from the Hey Arnold! theming being the absence of an equivalent to the Apathetic Frog helicopter.

The background music for the Slap City stage is also called "Traffic Jam" on the game's song selector (though the official Bandcamp release and the internal file names call the song "Noisy City" instead) and a side-scrolling stage reusing assets from Public Transit in Slap City's story mode is called "Traffic Jam".

Princess Remedy and Frallan, who are ex-girlfriends from their original game Princess Remedy in a World of Hurt, have a unique romantic team victory pose and can do a special healing kiss when one grabs the other and presses taunt. This will not work with Frallan's Nuna costume and Remedy's Princess Amelia costume.

When Orka uses her pummel, bone effects will come out of the victim. However, if Orka is pummeling Ittle Dew, she will only produce one bone, as Ittle only has one bone in her body in her original games.

The fifth recolor of the Goddess of Explosions' second alt, War Queen, is a reference to a Swedish holiday known as Saint Lucia's Day, where a girl or woman is chosen to dress with a wreath of candles, red belt, and white robe to represent the legendary Christian martyr Saint Lucia.

Slap City was originally envisioned as a mini-game in Ittle Dew 2 before being reworked into a full title. The scrapped mini-game had intentionally poor presentation, being locked to 30FPS with interlacing, something that was not retained in Slap City given it's focus on competitive play, and a low-poly style inspired by the original Super Smash Bros. The polygonal alternate form of Fluffy Fields, where the Clone Team is fought in arcade mode, is based on this version of the game.