The Showdown Effect is a side scrolling multiplayer action game inspired by action movies of the 1980s. The game features acrobatic movements and combat with both melee weapons and firearms. Movement options involve sliding, dodge rolling, swinging up and down from platforms, wallsprinting and ledge climbing. When using firearms it is necessary to aim directly at the enemy, aiming in front of or behind the enemy will not result in a hit. When using melee weapons it is possible to make a regular forward attack as well as an upwards attack. It's also possible to use the weapon to block incoming attacks. When running the player can do a dive. Diving onto an enemy incapacitates it for a short while. In addition to the starting weapons the player can also pick up common items found around the levels. These can then be used as weapons or for blocking. Items can also be thrown at enemies.
There are four game modes: team elimination, the expendables, one man army and showdown. In team elimination two teams compete and has to kill each other. When an entire team is eliminated the round ends and the team that is best of three rounds win. In the expendables one team is henchmen and the other expendables. The henchmen has to eliminate the expendables to end the round. Henchmen respawn quickly while the expendables' respawn time increases each time they die. In one man army the chosen player has to gain a score from killing henchmen who respawn infinitely. Once the one man army is killed another player will take his place. Showdown is a simple free-for-all game mode.
There are in total eight characters in the game. Two are available from the start and six more can be unlocked with points. Each character has its own special abilities but are otherwise equals. New items like weapons and clothing can also be unlocked. The game also features an in-game store where the player can buy items. These are visual variations of unlockable items and do not give any advantages while playing.