Contradiction with Matthew 8:30-32
In Mark 1:34, Jesus doesn't allow the devils to speak, whereas in Matthew 8:30-32, He permits them to speak and grants their request to enter the swine.
Matthew 8:30-32: And there was a good way off from them an herd of many swine feeding.
Contradiction with Mark 5:9-13
In Mark 1:34, Jesus forbids the demons from speaking, while in Mark 5:9-13, He engages in a dialogue with the demon Legion.
Mark 5:9-13: And he asked him, What [is] thy name? And he answered, saying, My name [is] Legion: for we are many.
Contradiction with Luke 4:41
Mark 1:34 states Jesus did not allow the devils to speak, yet Luke 4:41 mentions demons speaking to acknowledge Him as the Son of God before being rebuked.
Luke 4:41: And devils also came out of many, crying out, and saying, Thou art Christ the Son of God. And he rebuking [them] suffered them not to speak: for they knew that he was Christ. [to speak...: or, to say that they knew him to be Christ]