"Thankfully, they did share a behind-the-scenes sizzle reel, which looked like the type of video a studio would share with promotional partners to get them excited about the sequel. In the video, we saw director Andy Muschietti talk about what he hopes to accomplish with the anticipated sequel, saying it will be serious, more intense, and have scarier moments. The video also showed some pre-production artwork, including the different departments working on the film.
"Another part of the video showed new cast members Jessica Chastain, James McAvoy, Bill Hader, and others talking about what the film is about. There wasn’t much footage from the film, but we did see a shot of the cast together walking across a bridge.
"My favorite part, however, was some video from the very first table read. While we didn’t get to see the cast reading any lines, the video showed this massive table with every cast member listed getting ready to read the script."
Source: Comic Book
Thanks to Lou Sytsma