No movie fundamentally changed the horror genre as much as the original Halloween. The Shape’s iconic debut inspired — and continues to inspire — countless other slashers. And while most of these movies are only vaguely similar to Halloween, such as Friday the 13th, others were more blatant in their design and execution.

The flicks in question aren’t always set on Halloween, the victim doesn’t have to be a babysitter, and the antagonist may or may not even be masked. However, despite the superficial differences, these ten examples are unmistakably influenced by Michael Myers’ first killing spree.

Nightmares in a Damaged Brain (1981)

Nightmares in a Damaged Brain (or simply Nightmare) has a well-earned reputation for being sleazy and gruesome. Romano Scavolini‘s previous work in pornography comes out often in this erotic slasher, but if there’s anything to take away from this exercise in lust and grisliness, the gore scenes are meticulously set up and executed. As in most of the movies here, the killer has escaped a hospital and is out for blood. In this case, Baird Stafford‘s character has schizophrenia, and he’s been subjected to heavy drugs and experimental psychotherapy.

Trick or Treats (1982)

Gary Graver (also known as Robert McCallum) delivered perhaps the zaniest Halloween cash-in with 1982’s Trick or Treats. The movie begins with Carrie Snodgress‘ character having her husband (Peter Jason) committed to a psychiatric hospital against his will, and after a couple of years, he returns to get revenge on his ex. Meanwhile, Jackelyn Giroux‘s character is more afraid of the kid (Chris Graver) she’s babysitting on Halloween than his father, who’s now thrown on a nurse’s uniform and is bumbling his way toward their house! Trick or Treats isn’t an effective slasher, yet its weirder moments will make you laugh.

Alone in the Dark (1982)

Dr. Loomis fans will want to watch this post-Halloween slasher co-starring Donald Pleasence. A year after resuming his iconic role opposite Michael Myers in Halloween II, Pleasence played another psychiatrist in 1982’s Alone in the Dark. This time around, there are four killers (Jack Palance, Martin Landau, Erland Van Lidth, Phillip Clark) on the loose after a blackout frees them from a psychiatric hospital. The escapees then proceed to terrorize the family of another doctor from the same hospital. Jack Sholder‘s directorial debut not only adds more villains to the mix, it’s also a pioneer in the home invasion subgenre.

The Initiation (1984)

There was a small burst of dream-themed slashers starting in the early ’80s. A Nightmare on Elm Street is the most known example, though it technically came after (and eclipsed) The Initiation. When Daphne Zuniga‘s character is plagued by unsettling dreams, she and a grad student (James Read) conduct a sleep study to get to the bottom of these recurring nightmares. The terror escalates once the protagonist and her fellow pledges stay overnight inside a department store as part of their sorority’s initiation rituals. It might not seem clear how this slasher is particularly influenced by Halloween, but in time the inspiration becomes more evident.

Sorority House Massacre (1986)

Sorority House Massacre borrows from Halloween II as well as the original 1978 movie. In this slasher, which also uses the aforesaid dream theme, Beth (Angela O’Neill) is stalked by her homicidal brother, who’s freshly sprung from a — you guessed it — psych hospital. The setting is now a sorority house, and Beth shares a sort of telepathic connection with her murderous sibling. As unoriginal as it is, Sorority manages to scrounge up some decent suspense. There are two sequels, both of which are ridiculous in their own special ways.

Blood Rage (1987)

No holiday was left unturned as slasher filmmakers looked for new settings and gimmicks in the ’80s. With Halloween already taken, the folks behind Blood Rage settled on Thanksgiving Day. Ten years after a brutal incident at a drive-in theater, a man’s brother escapes from a psychiatric hospital to get revenge. He crashes his family’s Turkey Day festivities and carves them up. Blood Rage is regarded for its especially gory set pieces.

Offerings (1989)

By 1989, slashers weren’t as popular as they were earlier in the decade. This of course didn’t stop the stragglers from cropping up. One of these slasher slowpokes was Christopher Reynolds‘ underwhelming and poorly received movie Offerings. Here a man (Richard A. Buswell), once abused by family and picked on by his peers, returns to not only take revenge but also find the one girl who was nice to him back then. Offerings isn’t remembered by the masses possibly because it lacks the features that made earlier slashers so successful.

Happy Hell Night (1992)

In place of a sinister sibling or a random madman, the Canadian movie Happy Hell Night has a priest doing the killing. There’s also a supernatural angle to this panned slasher; the antagonist Malius (Charles Cragin) is practically demonic at the time of his first massacre on Halloween, and years later when he escapes his cell and picks off some unlucky college kids during hell night. Brian Owens‘ movie has been picked to shreds over its sloppy editing, paper-thin characters and barely there plot, but Happy Hell Night boasts some solid camerawork and creepy atmosphere.

Lovers Lane (1999)

As much as Lovers Lane is inspired by the new wave of teen-slashers, namely Scream, I Know What You Did Last Summer and Urban Legend, its basic plot better resembles that of Halloween. Here a Valentine’s Day massacre from years ago comes back to haunt a small town. The killer dubbed “The Hook” (Ed Bailey) was sentenced to life at a psych hospital for his crimes. In the present timeline, a new strand of murders suggest The Hook is back. ’90s slashers liked to keep the audience guessing, and Lovers Lane is certainly no different.

Frayed (2007)

No entry here copies and pastes the concept of Halloween more flagrantly than the indie slasher Frayed. This movie initially comes across as totally derivative, and the pacing can be a challenge. However, as the ending comes into view, Norbert Caoili and Rob Portmann‘s story takes on a whole new shape. What happens there in those last couple of minutes redeems the entire movie, not to mention becomes one of the more shocking twists of 2000s horror.