Contradiction with Matthew 27:27
Mark 15:16 describes the soldiers leading Jesus into the praetorium, while Matthew 27:27 portrays the soldiers gathering in the common hall.
Matthew 27:27: Then the soldiers of the governor took Jesus into the common hall, and gathered unto him the whole band [of soldiers]. [common hall: or, governor's house]
Contradiction with Luke 23:11
In Mark 15:16, Jesus is mocked by Roman soldiers, but Luke 23:11 describes Herod's soldiers mocking him, showing a different group involvement.
Luke 23:11: And Herod with his men of war set him at nought, and mocked [him], and arrayed him in a gorgeous robe, and sent him again to Pilate.
Contradiction with John 19:2
Mark 15:16 depicts the soldiers preparing to mock Jesus by leading him somewhere first, while John 19:2 states that soldiers had already twisted a crown of thorns on Jesus' head without mentioning a movement to another location.
John 19:2: And the soldiers platted a crown of thorns, and put [it] on his head, and they put on him a purple robe,
Contradiction with Acts 4:27-28
Mark 15:16 involves Roman soldiers mocking Jesus, whereas Acts 4:27-28 attributes the gathering against Jesus to Herod, Pontius Pilate, and others, including not specifically Roman soldiers, broadening the responsibility.
Acts 4:27-28: For of a truth against thy holy child Jesus, whom thou hast anointed, both Herod, and Pontius Pilate, with the Gentiles, and the people of Israel, were gathered together,