I'm looking for a short story that terrified me as a child. It appeared in a YA horror collection about monsters. None of the other stories stuck with me, but the one about “Mr. Monstro” kept me awake many a night.
It's the story of a boy who's caught outside alone at night. A mysterious voice warns him to stay in the light, because there's a horror lurking in the darkness named Mr. Monstro, a skeletal and murderous man. The story frightens the boy, who can't easily continue without leaving the pool of light he's standing in, so the speaker tries to comfort the boy and offers to escort him through the darkness. The boy is about to accept when he spots the man's skeletal hand. Before the boy can even object, the man starts protesting too much, claiming that he's not Mr. Monstro, just the unfortunate victim of a fire. . . .
I read this story around the same time as Scary Stories to Tell in the Dark (1981), but I don't think it was published in that collection – I think the story was actually titled “Mr. Monstro.”