Mulgarath

In 1928, Arthur Spiderwick finishes the Guide and hides it precisely so Mulgarath can't get it. The book holds everything Arthur learned about faeries, and in the ogre's hands it would be a weapon against all of them. Eighty years later, when Jared opens the Guide, Mulgarath comes sniffing around the house again.

Mulgarath doesn't work alone. His goblins, led by Redcap, kidnap Simon and surround the estate. The ogre can take any shape, which keeps him a step ahead of the kids, who never know who they're really looking at. To Mulgarath, the Guide is the key: with Arthur's secrets, he'd know how to control every creature in it.

On the full moon, the goblins use a potion to break the mushroom circle protecting the house. The family fights back with kitchen knives and tomato-sauce-and-salt bombs. Mulgarath walks in wearing the face of Richard, the kids' father. Jared stabs him and exposes the ogre. On the roof, Mulgarath turns into a raven to snatch the Guide midair, and Hogsqueal swallows him. Nick Nolte plays the ogre; Andrew McCarthy plays the father and the disguise.

In the 2024 series, Christian Slater is Mulgarath. In Henson, Michigan, the ogre poses as Dr. Brauer, Jared's therapist, with help from Calliope, a fetch. That keeps him close while Jared hunts for the pages of Arthur's guide. Slater won an Emmy for the role.

Critics weren't fond of the writing but praised Slater, who plays the villain charming and menacing at once. Reports said he signed on for season 1 only.

In the season finale, the siblings and their friends summon a troll that seems to devour Mulgarath. He comes back. The ogre takes Jared's form, and the real Jared ends up in the faerie realm. Showrunner Aron Eli Coleite said Mulgarath could return in a season 2, which hasn't been announced. The cliffhanger leaves the season open, with the ogre effectively living inside the Grace house, wearing one of the kids' faces.

In the books, Mulgarath takes a while to show up in person and wears a cloak. His plan goes beyond the Guide.