I'll start.
Did you know that Wil "Wesley Crusher" Wheaton's first credited acting role was Martin on the Secret of NIMH animated film? That was probably the last time he sounded assertive and tough in an acting role too, and he was both a little kid and a mouse. :rat-salute:
Whoever cut the trailer for Terminator 2 gave away the big reveal that the T-800 was sent back to protect John this time around. Cameron left it purposefully ambiguous until the moment in the mall hallway when he shoots the T-1000.
Somehow I had the pleasure of never watching or knowing the plot of Terminator at all, so when I watched Terminator 2 for the first time a few years ago I had no idea that Arnold was the good guy going in. The twist 100% worked and it was fucking awesome when I released what was happening. Really wished they didn't spoil it in the trailer so most folks could get the wonderful experience I had.
The trailer for Cast Away gave away that Tom Hanks made it back after being stuck on the island. This was done intentionally and Zemekis himself said something to the effect of "people want to know what happens in a movie before they go see it".
That's a great example of the difference between the two directors.