Melissa Leo , the Oscar-winning star of “The Fighter,” will appear in “The Mannequin,” a serial killer procedural from Sean Byrne, the twisted auteur behind “ Dangerous Animals .” Studiocanal’s new genre label Sixth Dimension is backing the film and will launch worldwide sales at Cannes. It will release the picture in the U.K., France, Germany, Benelux, Poland, Australia and New Zealand. Elevation Pictures will handle distribution in Canada. Byrne will write and direct and the film will head into production this summer. Leo’s credits include “Prisoners” and “Frozen River,” which earned her an Oscar nomination for best actress. She also appeared in “London Has Fallen,” “Flight” and “Conviction.” Byrne’s “Dangerous Animals,” a survival thriller involving a psychopath and sharks, grossed over $9 million worldwide on a budget of $2 million.…