Freddy Krueger is rendered powerless in Hell with Springwood forgetting him. Disguising as Pamela Voorhees, Freddy manipulates Jason Voorhees into killing Springwood teenagers to regain strength.
Lori Campbell lives with her widowed father, with friends Kia, Gibb, Trey, and Blake staying over. That night, Jason stabs Trey and folds him in half, with police suspecting Freddy. Following a nightmare, Blake awakens to his beheaded father before Jason kills him. The next day, police state it to be a murder-suicide, hoping to contain Freddy.
Lori's ex-boyfriend Will Rollins and friend Mark Davis are Westin Hills Psychiatric Hospital patients. They take Hypnocil to suppress dreams, due to them having the last contact with Freddy. A news report leads Mark to devise an escape plan. He and Will return to Springwood to tell Lori about Freddy. Mark later learns of the city's plan to eradicate Freddy and realizes they've nullified it. That night, Lori and the others attend a rave at a cornfield. A drunken Gibb believes she sees Trey and follows him to a silo - a dream trap set by Freddy. However, Jason kills her. Dismayed, Freddy realizes Jason's rampage will continue and deny Freddy victims.
Linderman and stoner Freeburg escape the rave along with Lori, and Kia. Lori confronts her father about her mother's death, lying to him. She and Will go to Mark's house, only to discover Freddy attacking Mark. Deputy Stubbs suspects a copycat Jason murderer, but his suspicions fall short. He approaches Lori and her friends, who piece together Freddy's plan. Learning of Hypnocil, they steal stock from Westin Hills, but Freddy possesses Freeburg and disposes of them. After electrocuting Stubbs, Jason is tranquilized by possessed-Freeburg, whom Jason bisects before losing consciousness.
The teens devise a plan to pull Freddy from the dream world into reality and force him to fight Jason. They take the unconscious Jason to Crystal Lake. Meanwhile, Freddy battles Jason in the dream world. He pulls him into a nightmare of him drowning as a child, learning his fear of water. Lori retrieves Freddy but he attacks her, revealing himself as her mother's killer.
Jason awakens and chases the others into a cabin. Linderman is mortally wounded and dies, the cabin ignites, and Lori is awakened, pulling Freddy into real life. Jason fights Freddy while they escape, throwing Freddy through another cabin's roof.
Lori, Will and Kia encounter Freddy. Kia distracts Freddy by taunting him until Jason suddenly kills her. As Lori and Will escape, the two begin to fight. The group attempt to ram a minecart into them, but both are knocked to the boardwalk. There, Jason tears Freddy's arm off while he stabs Jason's eyes. Lori and Will ignite propane tanks that blow Freddy and Jason into the lake. Freddy climbs out, but Jason impales Freddy with his own arm and Lori decapitates Freddy before Jason collapses.
Finally at peace, Lori and Will leave Crystal Lake together. However, Jason emerges holding Freddy's severed head, who winks at the audience and laughs.

Question: Why does Freddy Krueger need Jason Voorhees to kill?
Answer: To gain strength
Alternative answer: So that he can regain strength