Mads Mikkelsen’s the worst thing to happen to J.K. Rowling’s wizarding world since that snaky varmint Voldemort.

Replacing Johnny Depp after his various controversies, Mikkelsen’s a deliciously sinister delight as dark wizard Gellert Grindelwald in “Fantastic Beasts: The Secrets of Dumbledore” (★★★ out of four; rated PG-13; in theaters April 15). The third installment of director David Yates’ “Harry Potter” period prequel series still is overstuffed with characters and subplots, yet polishes a few missteps from previous films. There’s a renewed emphasis on magical creatures and another decidedly political bent to the franchise as it  digs into dark themes and offers a bewitching goofy side.

‘Fantastic Beasts’:Mads Mikkelsen’s Grindelwald declares war in ‘Secrets of Dumbledore’ trailer

Set in the 1930s, the new film continues the narrative that Grindelwald’s ready to go to war to eradicate the world’s Muggle (non-magical) population. He foments hatred among his followers and enacts a grand plan that will place him in control of the entire wizarding community through electoral means.

His former lover, Hogwarts headmaster Albus Dumbledore (Jude Law) can’t move against Grindelwald because of a blood oath between them. So he enlists the “Beasts” films’ primary antagonist, lovably awkward magizoologist Newt Scamander (Eddie Redmayne), to round up a “Dirty Dozen”-style crew of operatives for a counterintelligence mission to stymie the villain until they can strike back.

Along for the ride are Newt’s human baker pal Jacob Kowalski (Dan Fogler), brother Theseus Scamander (Callum Turner) and a new character, Lally (Jessica Williams), a Charms professor at the American counterpart to Hogwarts.

‘Fantastic Beasts’:Mads Mikkelsen talks stepping in for Johnny Depp

In the previous 2018 outing, “The Crimes of Grindelwald,” Newt took a back seat to young Dumbledore and a host of other characters. “Secrets” puts him back at center stage, in his natural habitat of looking for cool animals and being an all-around likable sort. There’s a daring rescue in which Redmayne does a wacky hip-swiveling dance with a bunch of baby scorpion things that’s so preposterous and silly it’s endearing.

All the movies from J.K. Rowling’s magical universe, definitively ranked

Law brings a mercurial side to Dumbledore that’s more in line with the version of the “Potter” films. Williams’ Lally is an enchanting new presence, while Jacob continues to be the comedic heart of this movie series: Kowalski’s goodhearted everyman aims to rescue his mind-reading love Queenie (Alison Sudol) – now a member of Grindelwald’s entourage – but finds time to have an enjoyable back-and-forth while lunching with some Hogwarts kids.