I left out the following sentences. Thank you.

1) In particular, he decides to gather a thousand friends in his castle. After five or six months of their stay there, he decides to hold a masked ball, which will take place in seven rooms.
2) The rooms are all set in a way that one cannot see from one room to another; besides, they all are in different colours but each room the colour of the glass of the Gothic window is the same as the colour of the ornaments.
3) Only the last one is all black with a red window. All the guests are enjoying themselves and dancing. However, when a clock with a pendulum strikes the hours, the orchestra stops playing and the people stop dancing, as if they were all frozen.
4) They all resume their activities as soon as the clock finishes chiming. When the clock strikes midnight a man, with a red costume covered in blood and a mask on his face that makes it look like the face of a dead man.
5) He moves to and fro with solemn movements. When Prince Prospero tries to stop him, he immediately dies. The same happens to his friends who try to touch him but realize there is no tangible form under the costume.
6) One by one all the people in the castle die and darkness falls all over the place.

1 answer

1. Remove "there" - or rephrase: After five or six months there...

2. I'm not clear on what you mean by this: "but each room the colour of the glass of the Gothic window is the same as the colour of the ornaments." Are some words missing? Or are there too many words (redundancy?)?

3. OK

4. Comma needed after "midnight" and not needed after "man" - wordiness: "a mask on his face that makes it look like the face of a dead man."

5. Clarify who the "his" and "him" are. Red Death? Prospero?

6. Comma after second "one" and after "die."