YouTube star Jason Ethier was texting on WhatsApp with a supernatural monster named Momo. Pacing his kitchen, Ethier followed Momo’s instructions, like filling a glass of water or writing Momo’s name over and over.

The monster seemed to know everything about Ethier, who has more than two million YouTube subscribers on his “ImJayStation” account. But when it came to Momo’s ultimate demand—that Ethier put a bloody kitchen knife to his own neck—Ethier refused.

“I can’t do it!” Ethier cried, throwing the knife to the ground.

“Everyone will pay for your actions,” the Momo account wrote back. “Unless they like and subscribe.”

Despite obviously being fake, Ethier’s “conversation” with Momo has earned more than 1.6 million views. An earlier video Ethier made talking to Momo on the phone also received more than 1.5 million views. So-called “Momo challenge” videos from other YouTubers, often done as part of the site’s “3 A.M.” genre of spooky videos, regularly receive millions of views too.

For views-hungry YouTubers, the Momo challenge has become a ticket to success. With its spooky backstory and viral potential, Momo is quickly becoming 2018’s version of the Slenderman internet legend, a story about a blank-faced creature in a suit that grew on online forums. In 2014, two girls stabbed a friend in an attempt to win favor with Slenderman. And like Slenderman, Momo-mania has a darker side, with the game potentially linked to the suicide of a 12-year-old girl in Argentina.

The Momo challenge and its signature image, a cropped picture of face of a bizarre bird-like image sculpture created by a Japanese special effects company, appears to have started earlier this year when a series of phone numbers with country codes for Japan, Colombia, and Mexico were posted to Facebook.

Whoever was behind the phone numbers didn’t respond to requests for comment from The Daily Beast, and the WhatsApp account went inactive in July. But reports online claim that the accounts would initially reply back with a series of escalating challenges. The requests culminate in a demand for the person texting with Momo to commit suicide, an echo of other viral urban legends, like the “Blue Whale Challenge” that swept Russia.

The Momo challenge first became popular in South America, according to Titania Jordan, the chief marketing officer at anti-cyberbullying company Bark.Us.

Since then, though, the tech-enabled urban legend challenge has spread to Europe and the United States, becoming a tool for anyone looking to harass someone or urge them to kill themselves.

“There’s a certain contingent of people that want to be the Momo,” Jordan said. “It started as one probably bored or disturbed person who was just sick, and now there are copycats.”

Someone contacted by the Momo could be dealing with someone on the other side the world. But they could be facing someone they know in real life, according to Jordan, who compared the Momo-related texts to a more dangerous, modern take on calling up a friend, posing as a stranger and freaking them out with details about their lives.

With the original Momo accounts inactive, the YouTube challenges featuring calls to Momo appear to be faked and often feature spooky images and jarring sound effects. Bored with WhatsApp, YouTubers have started to branch out, with some claiming that they’re using FaceTime to talk to Momo.

But Jordan says that, despite how absurd the idea of a bird-woman monster contacting people over text message may appear, the texting craze can be dangerous for children.

“It’s crazy, right?” Jordan said. “You hear about the Tide Pod Challenge and you think ‘how in the world would anyone do that?’”