To see the grim reaper in your dream signifies the negative, rejected aspects of your personality. It represents aspects of yourself that you have repressed. Alternatively, it symbolizes death. The dream may parallel an end to some situation, habit, or relationship in your waking life.
To dream that your friend has turned into the grim reaper implies that your relationship with them is dead. Your friend has changed into someone that you literally do not recognize anymore. Something has changed in the relationship.
To dream of the Grim Reaper represents closure or finishing. An aspect of your personality or a situation that forces transition. It may also reflect a situation in your life that is a omen of inevitable change.
Example: A girl dreamed of kissing the Grim Reaper. In real life she had finally decided on what she wanted to do after school finished. The intimacy with the Grim Reaper reflected her concern with exploring a career possibility that took away her fear of being a loser with bad job.