Death Curse of Tartu! (1967), the Hammer horror films, and El Santo being a demigod, Vengeance of the Mummy features Santo joining an expedition into the wild jungle to locate the tomb, and the treasure, of an Olpache prince. What they find of course is a mummy, and a serious bout of vengeance.
Vengeance is all pretty thoroughly entertaining. When you note that Santo is actually wrestling - I kid you not - a real fucking panther, you have to acknowledge that you're watching something fairly special. The poor cat ends up getting choked in the air by Santo and thrown, by the neck, a good distance. The panther sensibly flees after that, realising that in the great natural food chain Santo is listed just below 'utah-sized asteroid.' Santo's actually pretty uncharacteristically harsh in this film, as he genuinely threatens to kick the asses of the hired village folk who, legitimately afraid for their lives, want to abandon the expedition after the first mummy-related death. Santo aside, there's a good deal of murder going on in this movie. Old men getting murdered, women, mercenaries, assorted village folk. Everyone's at the mercy of the angry mummy and his decrepit arrows. The Olpache prince's vengeance and the presence of Olpache descendants among the village people actually partially hints at a political significance that bobs up to the surface just barely, one poking a finger at the white man's Imperialism, which lends Vengeance a gravity that most Santo films lack.
So: Good fun, the first Santo film I wholly liked, annoying bumbling professor aside. Ends off with a lame twist for an added bonus.