What are the differences between the three sentences?

The part “in films” is a nuance of vernacular. They are not asking if the person gets scared while being in a film, but instead are asking if the person gets scared while in a movie theatre watching a film. heresjohnny is correct: “Do you get scared watching films?” is proper and much less confusing.

English is a hard language to learn because there are so many words that sound the same but have very different meanings such as, two, to, and too. In your example you have three examples of poor questions. I will try to explain.

A) Have you ever got scared in films?

First this is improper grammer, it should read:

A) Have you ever been scared in films?

This question is referring to the past tense “Have you ever been”

The word ever is not needed but does indicate an idea and emphasizes the point

B) Do you ever get scared in films? is not a past tense question but the point of the question is the same

C) Do you get scared in films? is the best of the three as it is does not overemphasize the point

All three lack a specific however, the question should read:

Do you get scared watching horror films? Now that is proper English

;)

first one is past tense and other two are present tense