Contradiction with John 4:48
Mark 1:26 shows Jesus performing a miracle which might not align with John 4:48 where Jesus expresses frustration at people needing signs and wonders to believe.
John 4:48: Then said Jesus unto him, Except ye see signs and wonders, ye will not believe.
Contradiction with 1 Corinthians 14:33
Mark 1:26 depicts an unclean spirit creating a scene, which seems counteracted by 1 Corinthians 14:33, affirming that God is not a God of confusion.
1 Corinthians 14:33: For God is not [the author] of confusion, but of peace, as in all churches of the saints. [confusion: Gr. tumult, or, unquietness]
Contradiction with Matthew 12:19
Mark 1:26 describes a loud event, whereas Matthew 12:19 notes that Jesus will not cry out or shout.
Matthew 12:19: He shall not strive, nor cry; neither shall any man hear his voice in the streets.
Contradiction with Luke 4:41
While Mark 1:26 shows Jesus allowing the spirit to depart crying out, Luke 4:41 records Jesus rebuking the spirits and not allowing them to speak.
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]