Undercover Cops Gaiden: Hakaishin Garumaa is based on Irem's Undercover Cops arcade game. But whereas that title was a beat-em-up, Hakaishin Garumaa instead takes place as a turn-based board game RPG. Similar in design to the later Mario Party titles, players begin by choosing one of three of the undercover cops. The player begins at the start location of the board and must use one of their "numbered value tiles". If the number chosen is above 1, the player must compete on a slot machine to try to win a value up to what was written on the tile. Following that, the player is able to move the number value, which they have won, of spaces on the board. Certain squares will activate events that include talking with characters, buying items and engaging in battle.

Battles with enemies are handled by each side choosing one of the numbered tiles they own. The party with the higher number becomes the attacker and the lower value becomes the defender. Each side then chooses another numbered tile to determine the amount of "effort" put into the attack or defense as well as a position of the body to attack/defend. With that chosen, the turn's sequence plays out, with HP lost on a successful impact. Upon defeating an opponent in battle, the player gains XP and gold.