Splatoon is a third-person shooter set in a colour world where players control Inklings , characters that run around and shoot ink with a gun but can also transform into a squid to traverse through the ink. The game is controlled through the Wii U GamePad with the left analog stick for movement. Next to regular means to aim, gyroscopic motion control, by tilting the device, is supported with the right analog stick to look left or right and the triggers to shoot with a machine-gun like weapon and throw large bombs. Shooting ink colours the environment and the areas that are covered in a colour can be used to traverse quickly as a squid by transforming. In squid form the character cannot shoot, but moves quicker, can hide and can also scale vertical surfaces and swim through grates. Ink ammo is not unlimited and is refilled by transforming into a squid. Characters can jump, also in squid form with a more powerful dash jump. Enemies shoot ink in a different colour that covers the environment as well. This slows down the characters in regular form and cannot be swum through in squid form, so they need to counter it by painting it over with their own colour.
The game is set in Inkopolis that acts as a main hub. It offers access to different types of battles and characters that offer improved weapons and gear for aesthetic customization. By participating in battles experience is earned to level up along with a currency to buy new items. In the single-player part of the game Cap'n Cuttlefish asks to retrieve the Zapfish, Inkopolis' source of power, from the Octarians.
The game supports local one-on-one multiplayer matches in the Battle Dojo and online multiplayer games are divided into regular and ranked battles. Battles are played as four-on-four matches with two teams each with their own colour. Regular battles have the Turf War mode, while ranked matches have Splat Zones, a King of the Hill game type where teams fight to keep a certain area in the team's colour.
The game incorporates the Miiverse to post messages that appear in-game as graffiti on walls. Through Amiibo Splatoon sets additional missions can be unlocked, as well as additional equipment and a bonus mini-game after completion.