This piece of interview with Roger Corman on Joe Dante's work on trailers is my fawourite:

"Were there any elements that you had to tell Dante to tone down?

Not really. There was one memorable moment when Joe showed me a trailer for a picture just before lunch. I said, “Joe, it’s alright, but it isn’t quite as exciting as I would like it to be.” He said, “Let me work on it through lunch.” I came back after lunch, and it was exactly the same trailer, trimmed a little bit, with an exploding helicopter. I said, “Joe, that’s an exploding helicopter from a war picture we shot in the Philippines!” He said, “Well, don’t you think it helps the trailer?” It did. It was great. And I thought about it for a little while, and I figured, there’s no law that says every scene in a trailer has to be in the picture. So we left it in. After that, whenever Joe had a dull moment in a trailer, he would add the exploding helicopter."

Src, full interview

Fantastic 4: rise of the silver surfer.

Not only the trailer but during the whole movie there is this big build up to a reveal/fight of Galactus.

Was so hyped to see that by only be so disappointed seeing the silver surfer go in to the clouds and say "stop" and that was it...

Like what the fuck! Still salty about that one....

I didn't watch the trailers for it, but Click by Adam Sandler was supposedly marketed as another Adam Sandler comedy but was actually tearjerker drama with a medium heavy sprinkle of comedy.

Downsizing

From Dusk Til Dawn. I actually quite enjoyed the unexpected about-face in genre midway through the film, however.

Blade runner (the OG one), kangaroo jack (and a very similar trailer I don't remember with talking dogs?), Toys (maybe not exactly misleading per se, just chaotic as shit? Lots of hype but you had no clue what you were about to watch?), the village...

Definitely more, but most of it goes back far enough that I don't really remember enough specifics to place the shit.

I feel most might think about things that looked good but sucked, where as I always think about this:

I would have to say Kung Pow: Enter the Fist. Based on the trailers and the promotional material, I thought it really was just an old kung fu film brought to a NA audience for the first time or something. I had no interest in it. If not for my brothers wanting to go and my parents forcing me to drive them, I would never have known how God damn hilarious it actually is.

To a lesser extent, the original Austin Powers was the same, but I think it really just took the fact it spawned from a series of SNL skits for granted. I had never seen those skits, and the trailers made it look more like a romantic comedy about a guy who was just infatuated with, but not actually from, the 60's. I don't even recall it showing Dr. Evil in the trailers I saw on TV for it. Just some of the interactions between Austin and Vanessa.

Godzilla (2014) The trailer showed it as a Godzilla movie starring Bryan Cranston. Instead Cranston only had a brief cameo at the start of the movie and the whole movie was about a couple MUTO creatures, not Godzilla. Godzilla basically only had a couple cameos in the movie. I think most people who didn’t like it just didn’t like being tricked by the trailer.

Iron Man 3.

Led us to believe Ben Kingsley was going to be a badass villain only to be revealed that he was an actor.

Kangaroo Jack

They heavily featured the talking kangaroo that was only part of a short dream sequence in the movie.

District 9.

The movie trailer I saw before another movie made it seem like a standard issue shitty action movie. It was not.

2011s Drive, great movie, just not what they advertised.

Amazing no one has mentioned Bridge to Terabithia (2007). The screenwriters disavowed the trailers, iirc. Looks like a cute kids fantasy movie, starts out leaning that way with a middle-school Manic Pixie Dream Girl, then turns hard into being completely real life and extremely tragic. 14-year old me was not prepared.

Man of the Year (2006) looked like it was going to be a lighthearted Dave-esque movie about a comedic everyman president finding common sense solutions through his hijinks. It pivoted pretty quickly.

Pearl Harbor

Snow Dogs heavily marketed a couple of minutes bit so it seemed like the entire movie.

The trailer for Speed made it look like garbage when it was actually really fun.

https://youtu.be/8piqd2BWeGI?feature=shared

From what I've heard, Barbie 😅

Highlander: Endgame, original trailer showed the villain, Jacob Kell, as some kind of sorcerer. Suffice it to say, they removed all of the "magic" in the released film. The trailer can still be seen with a quick YouTube search.

Jurassic World Fallen Kingdom had a major part of the plot completely left out of the trailer, which I appreciated, but there were multiple suspenseful moments with the resolution in the trailer which was a bummer.

Vanilla Sky. I remember the trailers making it seem like it would blow my mind. Was so disappointed when I eventually saw it.

Mother! (2017) with Jennifer Lawrence was not even the same genre I thought it would be.