Question: For the original, the sequel and the remake, what materials did the crew use to create the blob and how did they get it to move?
Answer: In both the the 50's original and 70s sequel, the majority of the Blob effects were created using a thick silicone gel colored with red vegetable dye; its movement was essentially controlled by gravity, just letting the goop run downhill and angling the camera to provide the illusion that it was moving horizontally, vertically, or straight at the audience. The original film also employed a large barrage balloon (or weather balloon) covered in the colored silicone goop for shots where people are actually consumed by the Blob. The 1972 sequel additionally used a preposterous rotating spit covered in red plastic, mounted in front of the camera, to provide the Blob's point-of-view as it steamrolled toward its victims. The 1988 remake used much more sophisticated practical effects such as robotics, latex prosthetics, pneumatic tentacles, et cetera, which were directly inspired by John Carpenter's 1982 special-effects-heavy horror flick, "The Thing." For the last couple of decades, there has also been talk of a major CGI reboot of "The Blob," but it has yet to materialize.
Question: When Elliot Spenser is being transformed into Pinhead, who was cutting lines into his face and head and driving nails into him?
Answer: All we can see (in abstract closeup) is serpent-like tendrils cutting him and driving the pins into his head. As someone else said, it's likely another cenobite, although alternately it could also be the same "contraption" that turns Channard into a cenobite late in the film, given the tendrils are similar to the ones he sprouts.
Answer: Presumably another cenobite/cenobites. The choice not to show them makes for a better scene, as that moment is all about him, becoming the iconic Pinhead; the cenobites who made him that way are of no consequence to the story, and their own grotesque appearance would have distracted from his transformation.
Question: Who played the teenager that got killed at the gazebo? It looks like Michael J. Fox but, when I checked IMDB, there's no name listed for who played him.
Answer: The actor is Randy Doke. He's uncredited for the role, but IMDB lists him as "Puppet Show Dude."
Answer: I checked the Internet and read up on the Killer Klowns production and there is no mention of Michael J. Fox being in the movie. I do not know who the actor in the scene is, and while it's possible that it was Fox, it does not really resemble him, in my opinion.
Question: How can Jason go into the lake in Parts 6 and 7 if he's afraid of water due to drowning? He'd freeze up from the sight right?
Answer: Jason being afraid of water is not portrayed consistently throughout the series. Continuity between sequels was not a major concern when making this series.
Answer: I think that Jason is actually afraid of unpredictable situations with water. He is familiar with Crystal Lake after living in the forest for so long. He might be less hesitant to enter this lake sometimes.
Question: Why does Freddy use Alice to gain access to new victims?
Answer: As Kristin was being burned to death in the boiler, she passed her ability to pull other people into her dreams to Alice. This enabled Freddy to get new victims.
Answer: He'd killed her friends in the previous movie, remember? When he came back she'd had time to recover and make new friends.
That was Kristen, not Alice. Alice gives the answer to this question herself, while talking to Dan in the diner. She says that Kristen was the last of the children of the people who killed Freddy, and "maybe Freddy can't get to the new kids unless there's someone to bring them to him."
Question: Whatever happened to Scott, Donna's boyfriend? Donna and everybody else returned after Tangina left with Kane, but did he?
Answer: At the end of the movie, it was a different actress who played Carol Ann as the actress had already died by that point. Rumor has it that the actor who played Scott was so distraught over her death that he couldn't come back to film the scene.
Chosen answer: This isn't a mistake. John made the voodoo doll himself. When Chucky said he was "prepared" for it, he meant that he was prepared to do whatever it takes to get information from John about his being wounded. Even killing him as we see.