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One of the great horror movies of the 1960s is Mario Bava’s Black Sunday. In the opening sequence, a woman is accused of worshipping Satan, which she freely admits to doing. She suffers a terrible punishment (including having a spiked masked hammered onto her face), but before she dies, she swears she will return and revenge herself on the descendants of those who are sentencing her to death. I bring this up because this is pretty much the same plot as The Brainiac (or El Baron del Terror if you want the original Spanish).
In the opening sequence of The Brainiac, Baron Vitelius d’Estera (Abel Salazar) is accused of a host of crimes by the Mexican branch of the Inquisition. As he is about to be burned at the stake, he vows to return when the (extremely fake-looking) comet that is overhead returns, in 300 years. Since all of this takes place in 1661, you can guess that the Baron is coming back in 1961, essentially the film’s present day. And, because this is aping Black Sunday, the Baron has vowed to wipe out the lineages of all of his accusers.