EL MUNDO DE LOS MUERTOS ( THE WORLD OF THE DEAD) 1969 (released in 1970) aka SANTO AND BLUE DEMON IN THE WORLD OF THE DEAD
Santo (Caballero Enmascarado de Plata/himself), Blue Demon (Caballero Azul/himself), Pilar Pellicer (doña Damiana Velázquez), Betty Nelson (Aurora), Antonio Raxel (Chief Inquisitor/don Alfonso), Guillermo Bianchi (Bishop/Padre Francisco)
Directed by Gilberto Martinez Solares
The Short Version: Santo Goes To Hell is one way to describe this loco Lucha horror yarn that takes itself deadly serious in spite of the usual cheap effects and some blatant continuity errors and anachronisms. Santo not only battles a demonic Blue Demon, but also the living Lucha dead, and a gaggle of undead muscular minions with towels on their heads matched to mucho stock footage from HERCULES IN THE HAUNTED WORLD! If that weren't enough, Santo is savagely stabbed in the ring(!) leading to some graphic, and real open heart surgery footage(!!). In the next scene Santo is as good as new and slugging it out with the devil's disciples again(!!!). Strictly for schlock merchants and Mexi-movie lovers the world over.
In 1670, four members of a cult of devil worshipers are burned at the stake by Mexican Inquisitors. Damiana, a woman of nobility who is secretly the high priestess of the satanists begs help from Astaroth, Crown Prince of Hell. He sends Blue Demon to aid in her revenge. The Caballero in the Silver Mask suspects Damiana's treachery, and after refusing her lustful invitation to the dark side, she murders the Caballero's betrothed. Condemned to the same fate as her followers, Damiana lays a curse upon the descendants of her persecutors. 300 years later, the curse is visited upon Santo and his fiance, Alicia, by the demonic spirit of doña Damiana and her hellish minions. 
In what would appear to be a hodgepodge of ideas taken from some of the B/W Vergara Santo pictures from a few years earlier (most notably EL HATCHA DIABOLICA), EL MUNDO DE LOS MUERTOS is another Lucha horror title dealing with satanism, reincarnation, possession, and curses; and a film -- despite some grande schlock moments -- that has quite a bit going for it. For one, it's a precursor to the wildly popular THE MUMMIES OF GUANAJUATO (1970; released in 1972); a film that spawned several follow-ups, and featured Santo in a lesser capacity while giving the bulk of the limelight to Blue Demon and Mil Mascaras. 
Second, it has a strong romance angle for our Silver Masked savior. Ironically, the devil worshiping woman that coldly murders his buxom blonde bride-to-be in the 17th century segment ends up as his girlfriend during the modern day portion of the movie. In his earlier film career, Santo was mostly a wrestler with a second profession as a crime-fighter -- both of which kept him far too busy to maintain a social life with the ladies. Towards the end of the 1960s, he became more of a secret agent who wasn't so secret when it came to in-ring confrontations. Oddly enough, some of these later pictures had no wrestling bouts at all. They also replaced Santo's earlier Superman persona with a more emotionally libidinous one when it came to mingling with the fairer sex.
Blue Demon (Alejandro Munoz Morena) is co-billed alongside Santo
on the advertising, but he's reduced to what amounts to an extended
cameo in the actual film. He's seen during the first 30 minutes as Santo's hell-sent
nemesis, but returns during the last five to aid Santo, explaining that for this deed his
soul is now free after 300 years! This bit of movie backstory that Blue Demon was enslaved by Astaroth before winning his freedom after three centuries adds to his in-ring mystique given his name; mirroring the sideshow theatrics of American pro wrestling, only the wrestlers in this country never had film careers that replicated those of Mexico's Lucha stars. Hulk Hogan starred in several movies, but nothing to the degree of Santo, Blue, Mil, and some others.
Blue's return coincides with a
sequence wherein Santo goes to the title 'World of the Dead' to
save his girlfriend, Alicia. Possessed by the spirit of that persevering
demon, Damiana (who happens to look just like her), Alicia is unconscious and near death. If she dies, her
soul will remain in hell so Santo, with an hourglass inexplicably
deciding how much time she has left, makes the trek to the hot place
where the screen turns a red tint, and the landscape is home to stock
footage from HERCULES IN THE HAUNTED WORLD (1961). Both Blue and Santo
lob tree trunks(!) and huge rocks at the towel-wearing dead world
denizens in a bid to match up to the footage from the Reg Park classic. 
Not everything is lively in THE WORLD OF THE DEAD. There are several moments of sloppiness that are kind of at home in Mexican genre cinema if you're familiar with it. These moments tend to make EL MUNDO a more enjoyable experience. With the first thirty minutes taking place in the 17th century, virtually everyone in the film plays a dual role akin to Santo's character in EL HATCHA DIABOLICA (1965); but unlike that film, 17th century Santo looks totally out of place wearing his wrestling ring attire that's not even remotely concealed by the Colonial Era shirt and matching cape he's wearing. The same applies to Blue Demon and his familiar wrestling gear.
The fight scenes, while plentiful and fun, are on the mediocre side, and without variance. It's likely there was no actual choreographer and only one take was done. There are three recurring undead stooges that relentlessly assault Santo throughout the movie. During the period section, these three musketeers engage in a fencing duel with the Silver Knight. Santo was 52 years old at this time, and got around really well, but his skills with the rapier leave a lot to be desired. Thankfully for him, a trusty cross was hanging on his wall, successfully sending the musclebound trio packing.
Santo gets barely a chance for a breather as it's Blue's turn to pummel him into submission. This fight is much better and it looks like the two men are really working out some of their real-life frustrations with each other. Again, the sign of the cross repels the villain, accomplished by stopping and starting the camera accompanied by a puff of smoke that goes off a couple feet away from where Blue was standing. 
Arguably the most shocking, and unexpected sequence in this Santo showcase is the wrestling bout where he's Pearl Harbored once more by those three pale-faced villains. They pound Santo mercilessly, and in a surprising moment, the Saint is stabbed square in the chest with blood running out of the wound! The filmmakers then insert some gruesome open-heart surgery footage to insinuate Santo is being operated on. Astonishingly, a few minutes later, he's slugging it out with the three satanic stooges yet again. Considering this is Mexican genre cinema, anything is possible, and what follows is this films biggest faux pas....
In this sequence of Ed Woodian proportions, Santo is attacked once more by
Damiana's demonic and determined brawlers. They battle it out inside his home that has a modern 60s decor; but upon
taking the fight outside, the setting has suddenly, and inexplicably turned into what looks like an old western
town?! Elsewhere in the movie, there are some genuine location shots that adds some production value, but apparently a rural, or suburban area home (with a paved road) wasn't in the budget. There is no attempt to mask (haha) this glaring continuity error
at all. In Mexican genre films, you just have to accept this sort of thing, and especially in Luchador productions.
EL MUNDO DE LOS MUERTOS was the third and last of a trio of Santo movies made by prolific Mexican movie producer Jesus Martinez Sotomayor; the other two being SANTO AGAINST BLUE DEMON IN ATLANTIS (1970) and SANTO AND BLUE DEMON VS. THE MONSTERS (1970). Making 65 pictures between 1956 and 1970, Sotomayor cranked out at least one movie a month; reportedly a record in Mexico. EL MUNDO DE LOS MUERTOS is his last known credit. Some of the genre films on his resume include THE CASTLE OF THE MONSTERS (1958), THE SHIP OF MONSTERS (1960), MUSEUM OF HORROR (1964), LA LOBA (1965), and ADVENTURE AT THE CENTER OF THE EARTH (1965). He died in March of 2009.
The three Sotomayor Santo flicks are among the most enjoyable of the long running series, even if they're technically awful productions. If nothing else, they're lively (even if the antagonists are not!), colorful, and never boring. Those expecting a Santo-Blue team-up in EL MUNDO will be disappointed. Their onscreen interaction mirrors their offscreen rivalry with only a few minutes displaying the two working alongside each other. Interestingly, the Sotomayor's played off this rivalry in their three movies featuring the two superstars. Further, Blue has the least amount of screen time of the three Sotomayor productions he co-starred in. Successfully borrowing elements from past features, and adding some surprises of its own, EL MUNDO DE LOS MUERTOS (1970) is a place worth visiting for fans of Masked Wrestler movies.
This review is representative of the Lionsgate double feature DVD paired with SANTO EN EL MUSEO DE CERA (1963). There are no English options.