This is a story based achievement and cannot be missed, one that you'll likely get within minutes of starting a new game. Once you reach Pueblucho in the Darkest Timeline to receive the main story quest of seeking the three relics, you will be sent into Los Manglare. A few basic enemies and screens will be passed through until you meet up with Tostada.
*** Spoiler - click to reveal ***She will kill you to send you into the death dimension, allowing you to pick up the luchador mask one screen to the left and turn back into a legend.
Boom goes the achievement.