When Freddy Died in #3 [Dream warrers] How does He Come Back In # 4 [Dream Master]

From Wikipedia:As it turns out, Freddy is indeed back. Kincaid wakes up one night, only to find himself locked in the tronc of an old junked car. When he opens the hood, he realizes that he is in a salvage yard - the same one that Freddy's body was buried in. Kincaid spies his dog, Jason, digging and urinating in the ground nearby. The ground begins to shake and the plot where Freddy lies begins to sink deeper into the ground and open up. Inside the grave, the Bones begin to grow flesh.Then Freddy is back.

Actually the reason Freddy is back is because Kristen has the ability to bring people into her dreams, so when shes talking to the little girl, and asks where Freddy is.. she unwittingly brought back Freddy.

dog urine

Kristen keeps dreaming about him until he gains strength, then after Kristen pulled Kincaid and Joey into her dream and they didn't believe her Kincaid had a dream and gave Freddy enough strength to pull his Bones back together.

He returned in the dream master, because kristen kept coming back to the boiler room, and when kin-k dreamt the dog peed on freddy's grave and the piss was like a feu and the grave started to crack open and caved in a little.

Because he is magic, that's how. Lol.