Mii Force is a side-scrolling shoot 'em up game developed by Good-Feel. The game revolves around the Mii Force, led by the player, as they battle against the evil Gold Bone Gang. Players traverse each level blasting through enemies and recovering Miis encountered on StreetPass, who each provide unique weaponry based on their color. Miis are arranged on a grid of three forward facing weapons and one rear weapon, which can be rotated to shoot in multiple directions, with additional Miis powering up the main weapons when placed behind them on the grid. If the player is hit, one of the Miis will be forced to retreat, and the game ends if the player loses all of their Miis. After completing the main campaign, players unlock Arcade mode, which tasks players with clearing the campaign on one run. The game also features leaderboards, encouraging players to beat scores set by people encountered on StreetPass.