The Momo challenge character told one boy to 'put a knife to his neck' as part of the sick internet 'suicide' game.
The boy's shocked mum Lyn Dixon has warned parents about the Momo Challenge, a game which is played via WhatsApp, Facebook and YouTube, and encourages children to harm themselves.
It is characterised with an avatar of a girl with long dark hair and big bug-like eyes.
Lyn says her son, eight, has become frightened of the dark and of being alone, after images of the creepy Momo avatar popped up on YouTube when he was watching videos.
The mum, from Edinburgh, said: "He showed me an image of the face on my phone and said that she had told him to go into the kitchen drawer and take out a knife and put it into his neck.
"We've told him it's a load of rubbish and there are bad people out there who do bad things but it's frightening, really frightening."
The game has been linked to the death of a 12-year-old girl, from Argentina.
A French father filed a complaint with the State Department in November after his son took his own life.
And the Belgian Public Prosecutor's Office reported in November 2018 that a 13-year-old boy had been the victim of the "Momo Challenge" and hanged himself.
Lyn and her husband told their son's school of the concerns, prompting a talk about internet safety.
Lyn added: "It's a big fear, that we can't always control what he's exposed to on the internet.
"You read these stories about children committing suicide and we all know how difficult life is now with the pressures on children. Social media is a massive part of that. It's horrific and we've got no control over it.”
