I was rewatching ‘The Skydivers’ again, and, as always during the ‘Industrial Arts’ short, I didn’t recognise the narrator kid once he took off his glasses between scenes! Call it the Clark Kent Effect or my having the attention span of a goldfish, but it gets me every time.
So what other characters strike you as changing dramatically (or comically) over the course of an episode? Either through appearance or (god forbid) character development?
I nominate the woman from Robot Wars – I don’t remember anyone’s name except Stumpy – for Worst Most Ludicrous Change, from slapping Pilot McJagoff (yay) to snogging same (boo!).
Dude, I have this problem all the time. Beards really get me… if I am used to you with a beard, when you shave I don’t know who you are. Glasses confuse the heck out of me. I also have the attention span of a goldfish… the memory too: I sometimes forget what I am saying in the middle of a sentence.
As for striking changes, how about the Nanda lady in The Leach Woman… although I’m not sure if being played by two different people counts. The American lady changed a lot too, but that was makeup (and kinda weak makeup, although her alcoholism sold the look).
I think I missed something, or there might be a cut scene from the MST3K version, but I can’t believe how Joe Estevez goes from being himself to some vaguely European guy in the second half of Werewolf. I guess haircuts and clothes make all the difference.
I would have to say Lt. Col. Glenn Manning underwent the biggest change in an MST3K movie. One might even describe his change as colossal.
Kathy Ireland in Alien from LA has a literal Clark Kent Effect™ transformation… she loses her glasses and suddenly everyone realises she’s gorgeous. The helium detox programme didn’t go so well though.
The Great Vorelli turns into a ventriloquist dummy. His beard stays the same in both bodies, though.
I’ll be somewhat serious. I’m actually impressed by the growth the main character experiences in Gamera vs. Barugon. He’s not a terrible person in the beginning, but his focus is on making money and he’s not above doing it in a sneaky and underhanded way. By the end of the movie, he’s doing everything he can to fix what he did. I’ve said it before and I’ll say it again. That would have been a really great monster movie without Gamera. His idea with the mirrors was a good one.
But in terms of physical change, can you get more of a physical change than in Zombie Nightmare? He starts out as a 5-year-old kid, then, he’s an 18-year-old who is somewhat handsome and then he spends the rest of the movie as a more and more decayed zombie. By the end he even appears to have a bald spot! 
Mamie Van Doren in Girlstown.
Jan in The Brain That Wouldn’t Die. She loses 90% of her body by mass!
The actor himself acknowledged that Mikey from Teenage Strangler becomes way more emotional as the movie goes on, since he was trying to imitate the lead actress who he assumed was a pro (but was really a flight attendant).