Promotion to Parent: In the book, hers and Lisa's mother has died of an aneurysm. In the movie, she takes Lisa to live with her because their mother drinks too much, and Lisa's boyfriend is a bad influence.
Raven Hair, Ivory Skin: In the film, is a very pretty woman with pale skin and dark hair. The novel version is a redhead, though.
The Chick: Especially in the book, due to her age and inexperience. In the movie she's older, and more competent, knowing how to load and use a gun where her sister does not.
Distressed Damsel: Especially in the book, given her age. In both the book and the movie, the Wargle-replica attempts to molest her in the hotel bathroom.
Hormone-Addled Teenager: Both versions; the book opens with her arguing with Jenny about dating, and in the movie, she's gone to live with Jenny to get her away from a loser boyfriend.
Jerkass: He's a boorish slob who likes to use his badge to throw his weight around, and all his fellow officers hate him.
No Social Skills: Not that he cares. He's well-aware everyone hates him, but he's got job security so long as he doesn't screw up too badly.
Dr. Timothy Flyte
Cool Old Guy: This becomes very evident in Snowfield. He sounds like a kook, but he's very smart, and right.
Spared by the Adaptation: The Ancient Enemy kills him in the book, but in the film he survives and is later seen promoting his book on a talk show.
The Cuckoolander Was Right: Not that he was actually a cuckoolander, but his colleagues thought he was. Unfortunately, he was actually right.
The Worm Guy: He's the sole scientist out there to theorize that such events as the Roanoke disappearance and the extinction of the dinosaurs were the work of the Ancient Enemy, and as is usual of this trope by the time we meet him in the book he's been laughed out of academia, forced to write for boondock-supermarket-trash tabloid newspapers in order to pay the bills, and is shanghaied by the government because of the fact that his name was found written in blood on a wall and even then they keep sneering at his theories until it's too late.
The Ancient Enemy
Big Bad: Sees itself as the ultimate Big Bad, in that it believes itself to be Satan.
Eat Brain for Memories: Everything that the Enemy absorbs, it keeps the memory of. It's theorized by Dr. Flyte and the rest that the reason the Enemy believes itself to be Devil is because of so many humans absorbed that, in their final moments, believed it to be something unholy, so it pretty much started to believe its own hype.
Eldritch Abomination: Of a particularly horrifying variety. It can assume any shape it wants, can send multiple bits of itself off to torment its prey, can manipulate technology as it sees fit, and believes itself to be the Devil.