USA TODAY reveals Ed Helms and Patton Oswalt as the voices of villains Spleen and Mox in ‘Mune: Guardian of the Moon.’

Ed Helms, who voiced the delusionally heroic Captain Underpants this summer, heads to the dark side for his animated follow-up — the horned henchman Spleen in Mune: Guardian of the Moon.

Spleen and his evil cohort Mox (voiced by Patton Oswalt) are pulled into a plot to steal the sun in the critically praised 2014 French animated fantasy film that has been re-dubbed in English for a one-day release in the USA by Fathom Events on Aug. 12 (before heading to DVD and digital release this fall).

USA TODAY has first footage of the moronically malevolent duo as played by their U.S. star voices, along with Rob Lowe voicing Sohone, the hunky-and-knows-it heir to the Guardian of the Sun.

“Patton’s character and mine are a little bit like Flotsam and Jetsam in The Little Mermaid, part Abbott and Costello,” says Helms.  “We’re not smart, we don’t know what’s going on, but Mox is gung-ho and Spleen is terrified.”

USA TODAY reveals Rob Lowe voicing the self-loving Sohone in ‘Mune: Guardian of the Moon.’

The dim duo’s boss, the dark lord Necross, is the nefarious ruler of the Underworld and the real darkness in the fantasy film. Christian Slater voices Leyoon, heir apparent as the Guardian of the Moon, who inexplicably loses the job to a carefree faun named Mune, the film’s diminutive hero.

Helms says he fell in love with Mune after seeing the French-language version and “jumped to be a part” of voicing the misunderstood Spleen.

“He’s someone who has an evil job but a very sweet heart. He struggles to reconcile with that,” says Helms.

Director Alexandre Heboyan says he and his co-director Benoît Philippon were thrilled to “rediscover our characters with these voices. Each of them bring their own personality, with a great sense of comedy.”

Jack Fletcher, the director in charge of Mune‘s English dubbing, says recruiting Oswalt as Mox was a no-brainer.

“Patton’s an hilarious choice for a middle management/frustrated/backstabbing/boss-pleasing/brown-nosing character,” says Fletcher. “He latched onto the enjoyment of playing a superior, condescending bad guy and relished it.”

Animation voice actors usually do their work in tandem with the character creation, so for Helms, making Mune was more like replacing dialogue in post-production.

“You have to watch the scene, play it back and try to sync the words up with the character’s mouth,” says Helms, “Fortunately, my character’s mouth has very rudimentary movement.”

There was plenty of room for character expansion and creative license.

“Doing the translation, you had to reinvent the character a bit,” says Helms. “That’s part of the fun in the creative process. It’s exciting to see how everyone fills the vocal gaps and make the performances work.”

Lowe added a little cleverness to the self-absorbed Sohone.

“Rob came ready to play and have a good time,” says Fletcher. “He knew Sohone is his own biggest fan, and we came up with a voice for that persona.”

Helms is looking forward to seeing the just-completed English-language Mune for the first time.

“Mune is playful and enigmatic, with this tremendous artistic spirit about it. That’s why I wanted to be a part of it,” he says.