Vintage kids’ horror (?) book 1980s

I’m looking for a book my mother owned in the 80s in Australia. I remember it having a very dark black cover with the main image being a large, dripping/distorted skull. There was also a boy holding a candle walking towards the skull and the flame lit the side of the skull. It had many colors sort of reflected on it.

My brother says he remembers a scene from the book where the boy was in a large, mansion-style garden.