When my great nephew was 2 years old he had an invisible friend he called "my guy".
It all started when my niece bought a house in an older area of our city. It was a big two storey house that had been renovated into a lovely modern style with half of the upper floor transformed into a loft and the other half with a cathedral ceiling with skylight windows in the living-room. The staircase was moved in the process. When I saw it for the first time I loved it and was very happy for her as she had gone through a very difficult breakup and was now a newly single mom. I was also very surprised by the awesome deal she got on it too... It was far below the going real-estate market value.
She gave me the grand tour and we were standing in the kitchen when the decorative lights on the ceiling began flickering off and on. She said it just started doing that and I told her to get it checked out by an electrician as it may be a dangerous short. As we were discussing this I saw movement out of the corner of my eye. When I looked in that direction nothing was there but if I used my peripheral vision I saw what looked like the outline of a staircase and legs from the knee to the feet moving as if going down the steps. Whenever I tried to look at it straight on I would not see a thing. My niece looked at me strangely because I was acting odd but I said nothing because I did not want to freak her out and I really didn't feel frightened... I just thought it odd. Now this whole event was fleeting... Each sighting took seconds. I think she wondered why my eyes kept looking in that spot and she noticed the weird way I was looking... Standing still as could be and concentrating with my peripheral vision. This continued to happen every time I visited her. Finally she asked me why I was always looking in that spot when I was standing in the kitchen with her. So I told her. She said that was where the original staircase was; by the way, the electrician could not find any reason the kitchen lights flickered either.
The next odd occurrence was when her parents were visiting from out of town. Her dad heard someone unlatch the gate and walk to the back door. He waited for them to knock on the door but it never happened so he checked it out. No one was there. This happened frequently. I also heard it and so did my niece and her mom. We all found this stuff odd but it did not invoke fear.
Several months went by and her son, my great nephew, was now two. One day she was going down the steep steps from her loft bedroom with her son when he said, "mom wait for my guy." Great thought my niece with a smile, he has an imaginary friend. This went on for a while with her son playing and talking to his imaginary friend. One day she asked what his little friend looked like and he said, "He\'s not little he's a man." My niece said that sent a chill over her and she felt it was very odd. She told me about it and I agreed but we both decided it was best to just be low key about it with him.
One day they were going over to a close friend of my niece who his son called "auntie". As they were going down those steep loft steps again he said "wait for my guy!" My niece flippantly said, "Why is he coming with us?" her son then said, "can he!?" She said, "sure!" He then turned around and stared at nothing for a second then looked back at her and said, "He says he can't, he's never been there before." My niece thought this was a strange response from a two year old but not as odd as I did. She didn't know that a ghost cannot go to a place they had never been to when alive. When she told me this story the hairs on my arms stood on end but the strangest episode of all was when he was approaching three years old and out of the blue said, "mom, this isn't your house." My niece said, of course it is, mommy bought it." My nephew then said, "No it isn't my guy said it's his house and will always be his house." This freaked both my niece and me out. However it did not cause us to be fearful. For some unexplained reason it was not a scary entity nor was there a scary presence in the house.
After time my nephew's interest in his imaginary friend drifted off into obscurity. I recently had an experience when babysitting. I was watching TV and my nephew was fast asleep in his room. It was around midnight when I heard the gate being unlatched and someone came to the back door and knocked three times. I thought to myself, oh, my niece is home early! She must have forgotten her keys. I got up to answer the door but no one was there. I sat back down to continue watching TV and heard three more knocks but they were not as loud as the first time. The hairs on my arms stood on end but this time I said out loud in a firm voice "No, I am not going there with you!" I stayed where I was and continued watching TV and heard them for the last time... Three very faint knocks. Again I said, but this time to myself, nope not acknowledging you. The rest of the night was uneventful.
My niece did find out some history about her house from her real-estate. Apparently before the renos it was inhabited by an older woman and her two adult children, a girl in her twenties and a son approaching thirty. Her daughter committed suicide in the home over some guy but died later in the hospital. About a year later her son was killed in a car accident. She then sold the house. The house went from owner to owner and was finally renovated and sold to my niece. She still lives there. It has not frightened her to the point of moving but almost... Recently a thirty year old tenant who rented the basement suite was found dead in his kitchen. The police deemed it a natural death, causes unknown. She has always had trouble keeping the basement suite rented.