Donald Pleasence appeared in 137 movies; of those, I've seen just 30, but I'll hazard a guess that this is his worst film. Not only do I believe that Frankenstein's Great-Aunt Tillie must be the absolute nadir of Pleasence's career, I also reckon that it is the worst Frankenstein film ever made, the worst comedy ever made, and quite possibly the most terrible film I have ever seen (and I can regularly be found scraping away at the bottom of the cinematic barrel).
The script (if indeed there was one) feels like a stream of consciousness from a drunken Chinese madman, translated into English by another drunken madman whose first language is neither Chinese or English. The actors spout their lines of gibberish as though they're tripping on peyote (the film WAS made in Mexico, after all). Come to think of it, the whole experience felt like a bad hallucinogenic trip for me too, such is its sheer nonsensical nature.
Pleasence plays a descendant of Baron Frankenstein, who travels with Great Aunt Matilda (Yvonne Furneaux) to the ancestral estate to try and locate a hidden treasure and prevent developers from buying the place. In the basement of the castle, they discover Frankenstein's monster and bring it back to life. What follows is a series of seemingly random scenes in which everyone rambles incoherently whilst acting like fools.
Clocking in at an excruciating 100 minutes, Frankenstein's Great-Aunt Tillie is a virtually unwatchable mess that only the most dedicated fan of z-grade films will be able to finish. Those who do manage to stay the distance (and stay sane) will be treated to such garbage as women's rights protestors attacking the police with soda siphons, Pleasence dressed in a frilly maid's outfit, a parody of the Karloff classic's 'monster meets a little girl' scene that is off-the-charts insane, and an epilogue that continues the agony just when you thought it was all over.
Review by BA_Harrison from the Internet Movie Database.