Yasmin Ouard poses as Slender Man from the series "Mobile Hornets" ahead of the MCM London Comic Con Expo at ExCel in London, United Kingdom, Oct. 26, 2012. Getty Images

The Slender Man stabbing case, which grabbed headlines in 2014, took a new turn Monday when one of the two suspects, Anissa Weier, pleaded guilty to a lesser charge of attempted second-degree homicide as a party to a crime with the use of a deadly weapon, according to reports.

Two 12-year-old Wisconsin girls — Weier and Morgan Geyser — were inspired by the fictitious character, Slender Man, for allegedly stabbing their classmate Payton Leutner 19 times.

Weier initially faced a charge of attempted first-degree intentional homicide in the attack on Leutner, who narrowly survived the stabbing. The court accepted her plea and her case will move to its second phase where a jury would determine if she is guilty by reason of mental disease or defect.

Under the terms of the plea deal, Weier could be sentenced to 10 years in prison if the jury, at the next month's trial, concludes she was mentally competent and therefore legally responsible for the attempted murder. However, if the jury determines Weier was not mentally competent, she would have to spend three years in a mental hospital.

As of now, Weier faces 25 years in prison plus another 10 years of "extended supervision," reports said.

Weier's co-defendant Geyser was also due to appear in the court Monday afternoon. Nick Bohr‏, who works for ABC-affiliate WISN 12 News tweeted a photograph of Geyser's lawyer. The lawyer said he was "still negotiating a plea agreement, much like that reached with Anissa Weier."

Slender Man is a fictional supernatural character that originated in an online forum in 2009. He is a faceless man in a dark suit who is known to haunt children. But the stabbing case involving the Wisconsin girls sparked widespread debate about the character and its influence on children.

Here is what you need to know about the Slender Man stabbing incident of 2014.

1. Geyser and Weier discovered the character of Slender Man on Creepypasta Wiki, a website dedicated to internet horror stories. Both the teens believed he actually existed, and in early 2014, they decided to prove their dedication to Slender Man by becoming his "proxies." However, they thought they had to kill someone to prove their loyalty. Geyser and Weier decided to carry out the act on May 30 when the former had planned a sleepover for her birthday, according to the criminal complaint obtained by Newsweek.

2. In the following months, after both the teens decided to kill someone, they often talked about it among themselves. They used code words like "camping trip" to refer to the Nicolet National Forest in Wisconsin’s Northwoods, where the girls believed that Slender Man actually lived.

3. The victim was stabbed 19 times, and her liver, pancreas, and stomach were pierced with a deadly weapon used by Geyser and Weier, the suspects reportedly told the police.

4. After the incident, Leutner's parents asked for financial help in meeting medical bills on the crowdfunding website GoFundMe, setting a goal of $250,000, Chicago Tribune reported.

5. After the incident, HBO released a documentary "Beware the Slenderman" in 2016 that showed the story of Geyser and Weier committing the act to appease the fictitious character.