Answer to Question 1
Answer: Jung's archetype, the shadow, is the personification of the dark side of the ego and has some overlap with Sigmund Freud's id, a dark, sexual, and aggressive place. Your dark side can also be the opposite of your usual self, such as an introvert when you are usually an extravert.
Answer to Question 2
Answer: Freud's beliefs have been challenged and dissected over the years. Many of the theories are difficult to prove or disprove. Another problem is that his beliefs are not parsimonious (or straightforward).