Every episode of Grimm is borderline terrifying, but tonight’s Halloween-themed hour is especially so — and for guest star Kate del Castillo, the episode’s all-too-real villain “La Llorona” holds a special place in her nightmares. “Every single Mexicana has heard [the legend of] La Llorona,” Kate tells HollywoodLife.com of the Mexican folktale featured in the episode. ”It would scare the hell out of us!”

For those of you who aren’t properly educated in South American folklore, La Llorona is the ghost of a beautiful woman who killed her children to be with the man she loved — and as if that wasn’t tragic enough, the man still wouldn’t be with her. Now the spirit is said to be wandering the earth, seeking little children to snatch up. And that’s where Kate’s character, Valentina Espinosa, comes in.

“She’s a detective from New Mexico who’s obsessed with La Llorona because she lost her nephew,” Kate explains. “He was kidnapped under her watch, so for her, it became an obsession. That’s why she goes to Portland, to help the detectives find her. She knows the case.”

Juliette (Bitsie Tulloch) even gets to play translator and show of her Spanish-speaking skills, which Kate says are very impressive: “She did amazing!”

Kate’s appearance on Grimm is also meaningful to her as a Latina actress, because the episode will air in Spanish on Telemundo immediately after it airs on NBC. Kate recently starred on the Telemundo miniseries La Reina Del Sur.

“I’m their guinea pig,” Kate says. “Well, not me, but the episode. I think it’s genius! It’s time, and it couldn’t be better than with this episode, which is so Mexican. I’m honored and happy to be the one broadcasted by NBC and Telemundo for the first time.”

As an added bonus, we also have behind-the-scenes photos from the episode of Monroe (Silas Weir Mitchell) and his “haunted” house! (Oh, did you expect him to not be obsessed with Halloween?)

Grimm‘s Halloween episode airs at 9 p.m. tonight on NBC!

— Andy Swift

Follow @AndySwift

More Grimm on HollywoodLife.com:

1. ‘Grimm’ Video: What’s Next For Hank’s ‘Season Of Discovery?’
2. ‘Grimm’ Season 2 Video: Can Nick Handle His Mom AND Save Juliette?