Knock out all opponents! Extreme Thumb Fighter is a fighting game with a thumb-wrestling theme. The player picks an anthropomorphized thumb as their avatar to play against the game or a second player. The player doesn't have to stick with a bland thumb, which is known as Finger in the game. They can choose from a wide variety of funny characters, including Beanie, Dracula, Ester, Fishy, Granny, Hulk, Jack, Martha, Queen, Ragnar, Soldier, Techno, Topsy and Yoko. Each character has unique outfits or traits that match their names or stereotypes, such as a beanie hat for Beanie, a viking helmet for Ragnar and gray hair and a crown for Queen. During a match that consists of several rounds, the player must smack and bend and hold down the opposing thumb character long enough to deplete their energy and strength, which is displayed on a horizontal bar above them. Either combatant can quickly take control of the situation and move to hold down their opponent. The player must time their movements for the best results. To win a match, they must win three rounds. If they lose, their opponent giggles and "KO!" displays on the screen.