Arms is a 3D fighting sports game in which up to four players can control one of a variety of fighters, with the player able to perform basic fighting actions using extendable arms such as punching, throwing, blocking, and dodging. Arms features fifteen playable fighters, with some of them being released as downloadable content. Each fighter starts with three unique Arms that can be selected in battle, but the use of all other fighters' Arms can be unlocked in the Get Arms mode. All fighters also have unique attributes in combat. When the attack meter is fully charged, players are able to unleash a high-damage "rush attack" against their opponents. Players can also charge their attacks to temporarily increase damage and utilize elemental effects. Each character has a different set of abilities and unique Arms for different strategies. Players are able to use the system's Joy-Con motion controls or standard button inputs with controllers such as the Pro Controller to operate each Arm individually. Players are also able to customize their Arm load outs, with each Arm being able to be selected independently. Every Arm is different with elemental attributes and varying weights that affect gameplay. Up to four players are able to play in a single match, either in a three or four-way free-for-all, or in a two-on-two mode in which teammates are tethered together.
Besides the standard fighting mode, Arms features multiple other modes: Versus, Grand Prix, and a variety of Battle modes. In Grand Prix, players take on a set of 10 matches against computer-controlled fighters to win the championship belt. Battle mode consists of volleyball and basketball modes, a target breaking mode, and a survival mode. Players can also play online in a party match lobby with up to 20 players, or in one-on-one ranked matches.
Arms featured ten playable fighters at its launch: Spring Man, a boxer; Ribbon Girl, a pop star; Ninjara, a student ninja; Master Mummy, a resurrected mummy; Min Min, the poster child for her family's ramen restaurant; Mechanica, a girl fighting in a mech suit; Twintelle, a movie star; Byte & Barq, a robotic police officer and his robotic canine companion; Kid Cobra, a professional snakeboarder; and Helix, a lab experiment.
Characters from both Xenoblade Chronicles 2 and ARMS were going to appear but were cut due to bad timing, resulting in them being turned into costumes and spirits. (with Spring Man becoming an Assist Trophy)
When Spring Man is summoned, he’ll start attacking fighters with his Toaster Arms. His punches can outrange Simon’s and Richter’s whip attacks. His Attacks consists of a left and right punch and Flurry of Punches
Spring Man and Ribbon Girl were considered for new ARMS representation, but due to bad timing, they were turned into Spirits and Mii Costumes instead, along with Spring Man being an Assist Trophy. However, it was announced in a Nintendo Direct Mini later that the 6th DLC fighter will be from ARMS.