Fly Swatter is a minigame in WarioWare, Inc.: Mega Microgame$! that is based on a minigame from Mario Paint called Gnat Attack. The player controls a hand holding a fly swatter, which is moved around a backdrop by using the control pad. The player can move faster by holding down the button while moving. The goal of each stage is to kill one hundred enemies, by swatting them by pressing the button. The enemies include Gnats, which do not attack at all but are the fastest and hardest to swat, Big Flies and Dragonflies, which fire projectiles, and Bomb Flies which explode if left alone. An Extra Life appears at least once per level.
After defeating 100 enemies, Watinga appears; it takes several hits to kill and is the same every time. There are three levels, which repeat at a harder difficulty whenever all three are cleared.