A dream about a black dog means that it's challenging for you to control your desires.
If you see many black dogs, this indicates that you need to be more careful with your physical and mental health. You have to do something to prevent unpleasant situations that might surprise you.
When you dream about an angry black dog, this shows that you have to pay more attention and not neglect your life too much. You have to take better care of yourself. This dream signifies a warning of something scary happening in the future.
When you see a giant black dog, it shows that you want to achieve your goal by all means. However, life is not like that. It would help if you fought for your purposes, but you must remember the limits and norms in this life.