Material only in Mark:

2:13-21 The Flight to Egypt
3:19-21 Jesus' family thinks he is crazy
4:26-29 but compare Matt. 13:24-30
8:22-6 taking two attempts to heal a blind man
9:14-29 greatly expanded in Mark
14:51-52 the young man with the linen cloth flees

This is a short list since most of what is in Mark is also in Matthew and/or Luke.

Material not in Mark:

No Advent, or Christmas stories
No post-resurrection appearances of Jesus
Few parables.