Hi, I thought I will give a quick update even though it no longer belongs in this forum. My son has been able to give me a lot more details in the past few days, and he is very clear that this is not an imaginary friend but something he feared for some time. He seemed healthy and well in every other way, so we do not at this point think it is due to medical causes such as epilepsy or early bipolar etc.
He was able to recall that the first time he saw it was at his former church kindergarten and it began following his group of friends, and eventually just him. There is an old cemetary on the church ground facing the kindergarten and we have walked passed it many times. We are not members of the church and we have never went back since he left kindergarten. I have contacted the church and they recommend holding a special prayer for it to guide it onwards. Hopefully all will be resolved soon.