Acquiring every badge in the game grants one final unique badge for the occasion. However, many badges required for this achievement were only obtainable through the limited time Party Crash and Party Crash Bash events. As such, it is no longer possible to 100% the game legitimately, as the last event was held in April of 2020.

In Byte & Barq's render, there is an evident reflection of Spring Stadium in Barq's sunglasses. The applicable reflection in-game depicts whichever stage a match is being played on. On the character select screen though, this reflection is always of Sparring Ring, because it actually takes place on a duplicate copy of that stage meant for the character select screen, with a background hiding it from the player's view.

In ARMS' reveal trailer, the Sparky's lightning bolt graphic is absent during the live-action introduction. Despite this, the graphic can be seen on the gloves during the gameplay portion of the trailer.

Although the voices of the fighters are uncredited in-game, Nintendo has confirmed the majority of them through the official ARMS Twitter account:

• Peter Von Gomm voices Spring Man (and by extension Springtron).
• Momoka Kawasaki voices Ribbon Girl.
• Kenji Takahashi voices Ninjara.
• Kouji Takeda voices Master Mummy.
• Haruna Takatsu voices Min Min.
• Ayumi Fujimura voices Mechanica.
• Adeyto voices Twintelle.
• Ryouta Takeuchi voices Kid Cobra.
• Dominic Allen voices Max Brass.
• Soness Stevens voices Lola Pop.
• Toru Sakurai voices Misango.
• Donna Burke voices Dr. Coyle.

The remaining two fighters, Helix and Byte & Barq, are the only ones to have unknown voice actors. Coincidentally, they are also the only fully original non-human fighters.

In footage of a pre-release build of the game uploaded by Nintendo Treehouse, the Tribolt and Megaton retained their original Japanese names, Trident and Big Punch.

The Popper and Slapamander both had different designs in early gameplay footage. The former was originally orange with blue and yellow stripes, being green with yellow curls in the final game. The latter was initially black with orange stripes and a gold interior, as opposed to its final design's red-orange with white stripes and a blue interior.

In Byte & Barq's official render, there is a tiny portion of Byte's right thigh that is clipping into the back of his calf.

An unused, fully playable, ARM exists within the game's files under the name "GumShield." This ARM functions similarly to the Clapback, except incoming attacks stick to it instead of being reflected. The GumShield model also features a unique brand that went completely unused in the final game.

In an interview with Nintendo Minute, ARMS producer Kosuke Yabuki revealed that some employees at Nintendo of America found the initial sketches of Lola Pop to be frightening. Since coulrophobia (the fear of clowns) was uncommon in Japan, Yabuki felt like he had "learned a weak point of Americans."

In Master Mummy's official render, a clothing tag is erroneously featured on a strap across his chest. This tag is actually located on a strap upon his back in-game.

Although they remain uncredited, Bandai Namco contributed to the development of Mario Kart 8 Deluxe, Mario Kart Tour, and Arms.

The concept for Twintelle was presented when game director Kosuke Yabuki wanted a character that fought with their hair. To make sure she had a distinctly non-Japanese background, the designers spoke with people in different regions of Nintendo and gauged audience feedback.

To make the game stand out from other fighting games, the initial concept for the game had the camera positioned behind the player character. However, it was really hard for the player to judge distances. They solved this problem by making the arms extend, which led to the unique idea for the game.

The early idea of the game was to feature staple Nintendo characters such as Link and Mario. The aesthetic of the game clashed with them, and it was eventually decided that a new cast of characters be created. Character designs started with the arms first with the team working backward to decide what type of character would possess it. However, there are some exceptions where a design came first.

An early concept for the game had the characters using external devices to punch their opponents, however, this was later dropped in favor of the characters extending their actual arms.

According to the game's art director Masaaki Ishikawa, the Dragon Ball and Akira series were largely influential to the game's art style.