Dreams are works of the subconscious mind. Dreaming of your dead grandfather means that your subconscious communicates with your grandfather's wisdom and transmits it to your brain in the form of a dream, trying to make you realize it.
It's a good thing my dead grandfather can kill people. He didn't kill a real person, but the thoughts and impure thoughts in your head.
Generally speaking, this dream is a good dream, which shows that your subconscious and deep subconscious have communicated and blessed you unconsciously.