These are not unique to Mark, but helpful to consider when examining how Mark constructs his narrative.
Intercalation (putting two stories together in alternating passages)
3:20-35 Beelzebul, and controversy with Jesus' family.
5:21-43 Raising of Jarius's daughter and woman with the issue of blood.
6:7-44 Sending out of the twelve and Herod's banquet
11:12-25 Fig tree incident and Jesus in the temple
14:1-11 Jesus anointing for death and plotting against Jesus
14:53-15:15 Peter's denial and the trial of Jesus
15:6-32 Coronation of Jesus and the trial and execution
Questions
Ben Witherington quoted Fowler to the effect that there are 114 questions posed in the gospel with 77 of them going unanswered.
Doubles
6:21 - 8:26 the two feeding story cycles
8:31 - 10:52 with three weakly organized cycles (8:31-9:29, 9:30-10:31, 10:32-10-52)