Contradiction with Matthew 28:19
Mark 3:14 refers to appointing twelve apostles, suggesting a specific group, while Matthew 28:19 implies the Great Commission is for all disciples, not just a select few.
Matthew 28:19: Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: [teach...: or, make disciples, or, Christians of all nations]
Contradiction with Acts 1:21-26
Mark 3:14 mentions Jesus appointing the twelve, while Acts 1:21-26 involves the selection of a new apostle, suggesting the original number needed alteration or replacement.
Acts 1:21-26: Wherefore of these men which have companied with us all the time that the Lord Jesus went in and out among us,
Contradiction with John 6:70-71
Mark 3:14 describes Jesus appointing the twelve, but John 6:70-71 indicates one of them, Judas Iscariot, is a devil, suggesting a flaw or contradiction in the appointment.
John 6:70-71: Jesus answered them, Have not I chosen you twelve, and one of you is a devil?
Contradiction with Luke 6:13
Mark 3:14 speaks of Jesus ordaining twelve; Luke 6:13 calls this group apostles but gives no indication of them having any special ordination compared to a broad selection.
Luke 6:13: And when it was day, he called [unto him] his disciples: and of them he chose twelve, whom also he named apostles;