- Played by: Judah Lewis
- Action Survivor: He is smart and can come up with plans to defeat the cultists, though sometimes it's out of sheer luck he manages to survive.
- Afraid of Needles: He is REALLY not a fan of needles. When he gets a flu shot, he screams. When getting his blood extracted, he was straining very hard.
- All of the Other Reindeer: Gets bullied a lot in school from basically everyone.
- Determinator: Lampshaded by Allison to be one as she sees him fighting to cut the ropes trapping him in the chair.
- Loss Of Innocence: The events of the film force him to kill multiple people, and become very disillusioned with the one he trusted most.
- Precocious Crush: He has a big crush on his babysitter, Bee.
- The So-Called Coward: For an alleged "pussy," he shows a lot of bravery in situations that would make most adults faint with fear.
- Took a Level in Badass: By the end of the movie.
- Why Did It Have to Be Snakes?: Absolutely terrified of needles. Not very big on spiders either.
- Played by: Emily Alyn Lind
Cole's neighbor across the street and Only Friend.
- Childhood Friend Romance: By the end of the movie, she develops one with Cole.
- Covert Pervert: She's a sweet girl next door but she's very sexually curious, speculating about Cole's parent's sex lives and encouraging him to spy on his babysitter having sex.
- Girl Next Door: Well, across the street
- Hair of Gold, Heart of Gold: In contrast to creepy cult leader Bee.
- Nice Girl: She really has a good heart. Cole wishes every girl was like her.
- Only Friend: The only kid Cole's age who seems to like him.
- Deal with the Devil: The cultists are trying to make one to get their wishes fulfilled.
- Human Sacrifice: Part of their Faustian bargain involves sacrificing a human and mixing it with the blood of the innocent to get their wishes to come true. In the latter case, the "innocent" doesn't have to die. The former isn't so lucky.
- Teens Are Monsters: Crazy cultists, to be exact.
- With Friends Like These...: Are constantly snarking at each other and don't bat an eye when one of them is hurt or killed.
- Would Hurt a Child: None of them have any reservations about killing Cole when he finds out about their ritual.
- Played by: Samara Weaving
The cult leader, she works as a babysitter to gather blood of the innocent for her rituals.
- Affably Evil: She genuinely cares for Cole. She even kills Allison to save him.
- Alas, Poor Villain: She says that she used to be small and scared, but after using the book, she was confident, so although she kills people, it started as a way to be stronger. It looks like she dies after one last heart-to-heart conversation with Cole, who she really did care about, but when she tries to do their E.T. friendship signal one last time before dying, Cole denies it and leaves. She then sheds a few tears before dying.
- Ambiguously Human: At the end, the after-credits scene shows her suddenly leaping up and attacking one of the firefighters investigating the house.
- Antagonist Title: She is the babysitter in the title and also the Big Bad.
- Big Bad: She explicitly refers to herself as such to Cole, with a tear in her eye.
- Big Bad Friend: The main antagonist and Cole flat-out tells her he loved her after mortally wounding her.
- Broken Pedestal: Cole simply adores her, so the realization that she's an evil murderer hits him like a freight train.
- Car Fu: Cole defeats her by driving a car through his house to ram her.
- Cool Big Sis: If you ignore the "crazy cultist" thing, she's a pretty freaking awesome babysitter. Her very first scene shows her scaring the shit out of Jeremy for bullying Cole, and then giving Cole advice on how to properly defend himself.
- Even Evil Has Standards: She is surprised by how gory is a death caused by a shotgun, being very put off by Allison's death and claiming that is was too bloody.
- Not Quite Dead: Seemingly dies from her injuries after Cole hits her with a car, but The Stinger shows she survived.
- Only Sane Man: Insofar as anyone in the cult can be considered "sane." Compared to Max's senseless bloodlust, Sonya's creepiness, Amanda's vapidity, and John's Large Ham antics, Bee's got the most common sense of any of them.
- Pet the Dog: She saves Cole from a crazed Allison, even after previously shooting at him.
- Pragmatic Villainy: She opts to take Cole's blood via a harmless syringe, rather than killing him, since only a small amount of blood is needed. If she kills him, she has to find a new kid and start the whole process over. If she leaves him alive, she has a "fountain" of innocent blood. That said, it's implied she also leaves him alive because she does care about the kid.
- We Can Rule Together: Makes this offer to Cole at the end. He predictably refuses, burns her book and runs her over with a car.
- Would Hurt a Child: Zigzagged. She at first sends the rest of the cult to apprehend Cole, but ends up saving him from Allison. She admits that "there have been other children" when Cole asks, implying she has killed others before. While the kids may have lived since she seems to genuinely like the innocents she babysits for, another person is definitely required to die for the ritual first.
- Played by: Robbie Amell
A jock with a taste for killing, who joined the cult explicitly to kill people.
- Affably Evil: He's the most gleefully psychotic of all the cultists but his friendliness isn't faked, and he does have a bizarre moral code and acknowledges some of Cole's more badass moments, to the point where he tries to give him an "honorable death."
- Ax-Crazy: Out of all the cultists, he takes the most perverse joy in bloodshed and murder.
- Even Evil Has Standards: Sort of. Its implied that he detests bullying. He even spares Cole for a few moments when Coles house is being egged, and encourages (although a little forcefully) Cole to stand up to Jeremy.
- For the Evulz: He says that he isn't like the other cultists. He came just for the chance to kill people.
- Lovable Jock: Downplayed. Kinda. He's an Ax-Crazy psychopath who is positively gleeful about the idea of murdering people, so not exactly a good person. All that said, Max otherwise fits this trope well. He takes the time to help teach Cole about how to stand up to bullies and regularly compliments Cole for being badass himself. Not to mention being Affably Evil.
- Neck Snap: Dies when he falls off Cole's treehouse and gets tangled in a rope which breaks his neck.
- No Good Deed Goes Unpunished: In a manner of speaking, anyway. He wipes the egg yoke off of Cole's face before attempting to finish him off, claiming that Cole doesn't "deserve to go out like [that]". When the rotten wood he stands on breaks and he tries to grab a branch, the yoke makes his hands slippery and he falls, gets tangled up in a nearby rope, breaking his neck in the process.
- Pet the Dog: He decides to teach Cole to stand up to himself against a bully.
- Walking Shirtless Scene: Spends half the movie without a shirt. Lampshaded by Cole.
- Worthy Opponent: Seems to consider Cole one. He's impressed with him for blowing up Sonya, and gives him a headstart before he chases him and even tries to teach him to stand up for himself against Jeremy.
- Played by: Hana Mae Lee
A strange Asian girl who wears a beret.
- I'm Okay!: Hilariously subverted. She survives an initial explosion, says she's still alive, then is killed by a second explosion.
- Killed Mid-Sentence: After surviving the first explosion."I'm still alive, motherfu-!"
- Nice Hat: Wears a black beret.
- Nightmare Fetishist: Puts her finger in Allison's bullet wound just for the hell of it, and pauses in her pursuit of Cole to coo over a spider she finds.
- Tempting Fate: After an explosion, as soon as she claims to still be alive, a second explosion kills her for good before she can even finish insulting Cole.
- Played by: Andrew Bachelor
A wisecracking cultist.
- Black Dude Dies First: The first of the cultists to die.
- Bloody Hilarious: Gets totally soaked in blood.
- Disney Villain Death: Cole pushes him, causing him to slip on a toy car, and fall over the railing to his death.
- Faux Affably Evil: He's amusing in how he constantly tells jokes and suffers the most indignities among the cultists, but he's still an unrepentant killer.
- Played by: Bella Thorne
A shallow cheerleader who wants to be a journalist.
- The Cheerleader: She's a cheerleader and a nasty piece of work. She even wears the uniform throughout the movie.
- Jerk with a Heart of Jerk: Pretends to have a Heel Realization and gets Cole to lower his guard, only to try to kill him.
- Narcissist: She doesn't care so much that gets shot, but that she gets shot in the boob and it will ruin her physical appearance, which she values above all else, forever.
- Not Quite Dead: Appears to bleed out from a gunshot wound early in the movie, but wakes up to attack Cole later on.
- Redemption Rejection: Cole points out that even with one deflated boob, she can still live a rich, fulfilling life. Allison doesn't buy it.
- Your Head Asplode: Her death. She gets her head blown off with Bee's shotgun. Bee even lampshades how gory her death is. "Holy shit!"
- Played by: Doug Haley
A nerdy guy Bee invites to play spin the bottle with her friends.