This achievement requires the Three Enemigos DLC.
After you've obtained the Dimension Swap in the Badlands, return to Villachula. Go to the Mariachi club at the very top of the city to start the sidequest to return Panchito's guitar.
The first stop is in the second-eastmost house that has a single old woman inside; if you reach Rooster Ramirez, you've gone too far. The second stop is on the west side of the Dead side of town, who informs you someone else has the guitar. The third stop is at the fountain, so go to the fast travel statue and continue to move right and down until you're at the fountain.
At this point, change your costume to El Muñeco and visit the Mariachi club. They will inform you that Panchito has passed. Get the reward in the back, then swap dimensions to be on the stage. Press Y to perform and get your achievement!