Mariachi Undead takes place in a post-apocalyptic era in which the earth is full of deserts and a few major cities. The rich have fled to space colonies, and the poor struggle to survive. Our main character, Alfonso, is a mariachi player brought back to life with supernatural powers from the underworld. As Alfonso, you will traverse multiple environments to find your son. Along the way, Alfonso encounters his old band mates who help him.

The game uses a unique cover system in an action side-scrolling environment. Alfonzo has an arsenal of magical weapons at his disposal, such as his Soul Pistol. With endless ammo, his magical pistol can remove the enemy's soul to replenish his own health and charge his power. He can slide into cover to avoid enemy fire. If Alfonzo gets completely overwhelmed by enemies, he can do a special rhythm attack by playing his magical guitar. The player can complete a rhythm sequence using a Rhythm Guitar, or a unique rhythm experience using a controller. Depending on the percent correctly achieved, the player will AOE (Area of Effect) the enemy.