Mercenary Kings is a 2D arcade run-and-gun game with graphics similar to Scott Pilgrim vs. The World: The Game. The gameplay is somewhat similar to the Metal Slug series, but levels are less linear in design. The player chooses from two main characters, King and Empress, who can be customized. In their base, they can interact with other characters, buy items, and take on missions assigned by the leader.
The mission objectives vary, with goals including destroying structures, retrieving items, rescuing people, and killing enemies. The character has two primary weapons: a gun and a knife. However, the gun requires frequent reloading. The game features cooperative multiplayer, both online and offline, allowing friends to play together on their Nintendo Switch.