You can get a sequel to one film. Glass is a sequel to two different movies that span several decades and different production companies. Split (2016) and Unbreakable (2000).
David Dunn (Bruce Willis) is the vigilante who plans to catch Kevin Crumb (James McAvoy) the man with multiple personalities including the Beast, who has abducted four cheerleaders. After a showdown both get captured and sent to Raven Hill Memorial hospital which has been adapted to keep them both locked in their rooms.
Also inside the hospital is Mr Glass (Samuel L Jackson) almost comatose filled with drugs and confined to his wheelchair because of his brittle bones. The man who killed hundreds to prove a theory that some people had extraordinary powers. The kind of powers you find in comic books.
Dr Ellie Staple (Sarah Paulson) has been sent in to show these three people that they are normal people, their abnormal frontal lobes making them think they have superpowers.
M. Night Shyamalan after his initial success with movies like The Sixth Sense and later flops such as The Happening. He went back to basics and re-invented himself through low budget independent horror/thrillers. It culminated in the critically acclaimed Split.
In Glass, Shyamalan pits Dunn against the Beast but it is also a tease. The film is called Glass. Watching and waiting is Elijah Price/Mr Glass. He has woven a web, his body is weak but his mind is sharp. That is his superpower. His past actions has led to the present and he envisages a comic strip superbattle.
Shyamalan has made the movie he wanted to make. The pace is deliberate, it alludes to comic book conventions but without taking the Marvel Films route. I thought it was wonderful even if the movie had faults.