It never happened. Bela Lugosi never made a film in Mexico, but it could very well have happened had Lugosi lived past 1956. Indeed, it's highly probable that Lugosi would have been easily seduced to make horror films in Mexico just as several of his compatriots in American horror films had been. Lon Chaney Jr. was the first American horror legend to make a Mexican film, La casa del terror (1959). In that film he played not only a mummy, but a werewolf, with make-up similar to his famous portrayal of Lawrence Talbot in Universal's classic horror series of films in the 1940s. Lugosi's "rival", Boris Karloff, made four films for Mexican producer Luis Enrique Vergera during the spring of 1968, though because of his emphysema, he had to film his scenes in Los Angeles. Basil Rathbone, Lugosi's co-star in Son of Frankenstein (1939) and The Black Sleep (1956), succumbed to the need for money with Autopsia de un fantasma, (1967) a lighter touch Mexican fantasy. The American horror star with the most credits in Mexican fantastique is, no surprise, John Carradine, who reprised his Dracula role in Las vampiras (1968) and made four more Mexican films, Autopsia de un fantasma, La Senora Muerte (1967), Pacto diabolico (1968), and Enigma de muerte (1968).
Lugosi's death came right before the explosion of Mexican horror in 1957 when El vampiro became such a success, with German Robles in the role of the vampiric Count Lavud. One wonders if Lugosi himself would have been solicited for this role by producer Abel Salazar, but even if he had not been, the upswing in horror film production in Mexico would have meant that Mexican film producers would have sought the original Dracula actor and horror king to star in their films. Undoubtedly, someone would have had the predictable, but certainly thrilling thought of having Lugosi appear as the legendary fright character, Dracula himself. Given how many of the Mexican horror films of the 1950s imitated a Universal feeling (even going beyond the Universal films in atmosphere in several films), any appearance by Lugosi in a Mexican horror film would have pleased many horror fans and reinvigorated Lugosi and his career. Had Lugosi lived into the 1960s, it's probable that a Mexican horror film in color, with Lugosi as Dracula, would have been made. This would have been a realization of one of his latter day goals--an appearance in a color film as his most famous character.