The following is a list of demons, vampires, human monsters, walking dead, ghosts, beasts and any kind of evil being or supernatural creature seen in the Buffyverse (created by Joss Whedon).

Demons, Half-Demons and Old Ones

Acathla ("Becoming, Part Two")
Ano-Movic Demons: The Straleys ("Bachelor Party")
Anyanka
Arney ("Offspring", "Lullaby")
Artode ("Life of the Party")
Assassin demon ("Sanctuary")
Avilas ("Help")
Baker ("The Ring")
Balthazar ("Bad Girls")
Barney the Empath Demon ("Parting Gifts")
The Beast
The Beast of Amalfie ("To Shanshu in L.A." and "Birthday")
Billy Blim ("That Vision Thing", "Billy")
Bohg'Dar Demon ("Salvage")
Boone ("Blood Money")
Boretz Demon ("Power Play")
Brachen Demons ("Hero")
Bringers
Bro'os ("Teeth") the Loan-Shark demon ("Tabula Rasa")
Brotherhood of Seven: Marc ("The Puppet Show")
Senator Helen Brucker
Cantonese Fook-Beast ("That Vision Thing")
Carlos ("Underneath")
Carnyss Demon ("Judgment")
Chaos Demon ("Fool for Love")
Champion Knight ("Judgment")
Clem
Codger Demon ("Heartthrob")
Connor
Cordelia Chase (became part-demon, never used powers for evil)
Covenant of Trombli: Silas, Barshon
Cyvus Vail
Deevak ("First Impressions")
Devlin ("Life of the Party")
D'Hoffryn
D'Hoffryn's acolytes in Arashmahaar ("Something Blue")
D'Korr (D'Hoffryn's second demon hitman) ("Get It Done")
Doc
Doyle
Drokken Beast ("Belonging")
Drug Lord Demon ("The Prodigal")
Durslar Beast ("Fredless")
Durthok the Child-Eater ("Judgment")
Eater Demon ("Slouching Toward Bethlehem")
Eli ("Harm's Way")
Eyghon the Sleepwalker ("The Dark Age")
Ethros Demon ("I've Got You Under My Skin")
Fell Brethren
Dr. Fetvanovich ("Quickening")
Flanjoid Demon ("To Shanshu in L.A.")
Francis ("Release")
Frocter Demon ("Release")
Sid & Monica Frzylcka ("Double or Nothing")
Fungus Demon ("The Harsh Light of Day")
Fyarl Demon ("A New Man")
Gachnar ("Fear, Itself")
Garwak Demon ("Provider")
Gathwok Demons: Vakma, Trensiduf ("Over the Rainbow")
Gavrok Spiders ("Choices")
The Gentlemen and their Silent Footmen ("Hush")
Ghora Demon ("Forever")
Glarghk Guhl Kashma'nik Demon ("Normal Again")
Glory's Minions: Jinx, Dreg, Murk, Slook, Gronx and the High Priest Minion
Glurgg ("Apocalypse, Nowish")
Gnarl ("Same Time, Same Place")
Goran Demons ("The Girl in Question")
Granok Demons ("Forgiving")
Grappler Demons ("Quickening")
Grimslaw Demon ("Selfless")
The Groosalugg
Grox'lar Beast ("Just Rewards")
Hainsley Demon ("Just Rewards")
Haklar Demon ("Belonging")
Halfrek
Hans and Gretta Straus ("Gingerbread")
Haxil Beast ("Expecting")
Hellhound ("The Prom")
The Hellions: Razor, Mag, Klyed ("Bargaining", Parts One and Two)
Hellmouth Spawn ("Prophecy Girl", "The Zeppo")
Hindu Kush ("Judgment")
Howler Demons ("The Ring")
Illyria
Intestine demon ("Lonely Hearts")
Izzerial the Devil
Jenoff the Soul-Sucker ("Double or Nothing")
Jenoff's Repo-Man ("Double or Nothing")
Princess Jheira and the Oden-Tal females ("She")
The Judge ("Surprise"), ("Innocence")
Kailiff demon/Griff ("Rm w/a Vu")
Kamal the Prio-Motu Demon ("Judgment")
Karathmamanyugh Demon ("Spin the Bottle")
Kathy Newman/Mok'tagar demon ("Living Conditions")
Kek Demon ("I've Got You Under My Skin")
Ken and the demon enslavers ("Anne")
Der Kindestod ("Killed by Death")
Kith'Harn Demons ("Origin")
Kleynach Demon ("Reprise")
Kovitch Demon ("She")
Kulak of the Miquot Clan ("Homecoming")
Kungai Demon ("Parting Gifts")
Kurskov's minions ("Waiting in the Wings")
Lachnie Hag ("Benediction")
Lagos ("Revelations")
Lasovic ("The Ring")
Lei-Ach Demons ("Family")
Lilliad Demons ("Dad")
Lissa ("First Date")
Lister Demons ("Hero")
Liz ("Judgment")
Lohesh (mentioned in "Graduation Day, Part One")
Lorne's Id Monster ("Life of the Party")
Lubber Demons ("Happy Anniversary")
Lurconis ("Band Candy")
Lurite Demon ("Heartthrob")
Machida ("Reptile Boy")
Madam Dorian and her Girls (Lina) ("War Zone")
Mandraz ("Wrecked")
M'Fashnik Demon ("Flooded")
Mayor Richard Wilkins III aka Olvikan
Mellish ("The Ring")
M. James Menlo ("The Shroud of Rahmon")
Merl
Mofo Demon (Lenny Edward's demon muscle) ("War Zone")
Mohra Demon ("I Will Remember You")
Moloch the Corruptor ("I, Robot... You, Jane")
Mordar the Bentback ("Judgment")
Mucus Demon ("Double or Nothing")
Multi-headed demon ("Supersymmetry")
Mutite Demon ("Heartthrob")
Nahdrah Demons ("Provider")
Nezzla Demons ("Judgment")
Norman Pfister ("What's My Line", Parts One and Two)
Nurbatch Demon ("That Old Gang of Mine")
Octarus (""What's My Line", Part Two)
Olvikan ("Graduation Day, Part Two")
Ovu Mobani ("Dead Man's Party")
Piasca demon ("Lonely Hearts")
Pockla Demon ("Dead End")
Polgara Demons ("The I in Team")
Prechian Demon ("The Thin Dead Line")
Preggothian Demon ("Blind Date")
Pyleans: Lorne, Constable Narwek, Landok, Numfar, Blix, Lorne's Mother (Deathwok clan), Pylean Royal Guard: The Captain of the Guard
Queller Demon ("Listening to Fear")
Quor-Toth Demon ("The Price")
Rahmon ("The Shroud of Rahmon")
Reptilian Demon ("Parting Gifts")
Rodentius Demon ("Fredless")
Rwasundi Demons ("Dead Things")
Sahjhan
Sahrvin Demons
Sathari ("Power Play")
The Scourge: Trask, Tiernan ("Hero")
Archduke Sebassis
Sebassis' Slave/Pee-Pee Demon
Senih'D Demon ("Couplet")
The Senior Partners of Wolfram & Hart
Serparvo Demon ("Something Blue")
Shorshack Demon ("I've Got You Under My Skin")
Sloth Demon ("Judgment")
Sorialus the Ravager ("Waiting in the Wings")
Shur-Hod Demons ("Heartthrob")
Sisterhood of Jhe ("The Zeppo")
Skench Demon ("Double or Nothing")
Skilosh Demons ("Epiphany")
Skip
Skyler ("Enemies")
Slime Demon ("The Wish" & "To Shanshu in L.A.")
Dr. Gregson the Slod Demon ("Heartthrob")
Sluggoth Demon ("Beneath You")
Smile Time Puppet-Demons: Polo, Ratio Hornblower, Flora, Groofus ("Smile Time")
Soul-Eater ("Calvary")
Stewart Burns ("Hell's Bells")
Strom Demon ("Release")
Suvolte Demon ("As You Were")
Sweet ("Once More, With Feeling")
Sweet's Lackeys ("Once More, With Feeling")
Tarval Demon ("Expecting")
Talamour/Burrower ("Lonely Hearts")
Taparrich and the Mok'tagar demons ("Living Conditions")
Tezcatcatl ("The Cautionary Tale of Numero Cinco")
The Thaumogenic Demon ("After Life")
Thesulac Demon ("Are You Now or Have You Ever Been")
Thraxis ("Life of the Party")
Tien Shenin ("Judgment")
Tom Cribb ("The Ring")
Tor ("The Trial")
Torto Demon ("Happy Anniversary")
Torg ("Showtime")
Toth ("The Replacement (Buffy the Vampire Slayer)")
Tough Guy Demon ("That Old Gang of Mine")
Tree Demon ("Couplet")
Turfog the Thrall Demon ("Dear Boy")
Vahrall Demons ("Doomed")
Vajnu Demon ("The Shroud of Rahmon")
Val Trepkos ("The Ring")
Vampire Detector Demons ("Blind Date")
Vartite Monster ("Judgment")
Vigaries ("She")
Vinji Demons ("Harm's Way")
Vocah, Warrior of the Underworld, Bringer of Calamity ("To Shanshu in L.A.")
Voynok Demon ("Supersymmetry")
Vyasa ("The Shroud of Rahmon")
Wan-Shang Dhole ("That Vision Thing")
Wainakay Demon ("Happy Anniversary")
Wolfram & Hart Failsafe Technician Demon ("You're Welcome")
Wolfram & Hart Torturer Demon ("Underneath")
Wraithers ("Loyalty")
Whistler
Yeska the Davric Demon ("Guise Will Be Guise")
The Zealots of the Devourer: The High Priest Zealot, the Keeper of the Name ("Sacrifice", "Peace Out")

Vampires

Absalom ("When She Was Bad")
Alonna Gunn
Alphonse ("Doppelgangland")
Andrew Borba ("Never Kill a Boy on the First Date")
Andrew Hoelich ("Anne")
Angel/Angelus
Anne ("Lies My Parents Told Me"), Spike's mother
Aurelius, who prophesied the coming of the Anointed One
Big Ugly
Billy Fordham ("Lie to Me")
Blair ("Helpless")
Boone ("Who Are You?")
Charles Gunn ("After the Fall")
Charlotte ("Sleeper")
Collin, the Anointed One
Dalton
Darla
Doug Sanders
Dracula ("Buffy vs. Dracula")
Drusilla
El Eliminati ("Bad Girls")
Elisabeth
The Gorch family: Lyle, Tector, and Candy ("Bad Eggs", "Homecoming")
Harmony Kendall
Holden Webster ("Conversations with Dead People")
James
Jamie ("Pangs")
Jay-Don ("The Shroud of Rahmon")
Jeff & Mutt ("Crush")
Jesse McNally
Julia ("Lie to Me")
Kakistos ("Faith, Hope & Trick")
Stephen Korshak ("Some Assembly Required")
Lean Boy
Lenny ("Lovers Walk")
Luke
Marcus ("In the Dark")
The Master
Nightmare Buffy ("Nightmares")
Nostroyev ("Why We Fight")
Prince of Lies ("Why We Fight")
Rebel Vampire Posse: Carl, Justin, Zack, Glenn, Christy, Marla and others ("All the Way")
Richard ("Lies My Parents Told Me")
Russell Winters ("City Of")
Sam Lawson ("Why We Fight")
Mr. Sanderson ("Gingerbread")
Sandy ("Doppelgangland", "Family", "Shadow")
Sarah Holtz
Spike
Sunday and her gang: Dav, Rookie, Tom, Jerry and Eddie ("The Freshman")
Theresa Klusmeyer ("Phases")
Thomas ("Welcome to the Hellmouth")
The Three ("Angel")
The Three Sisters ("Buffy vs. Dracula")
Tom ("The Harsh Light Of Day")
Mr. Trick
Turok-Han vampires
Ul'thar Vampires
Whip and the Hooker Vamps ("Into the Woods")
Wishverse Willow ("The Wish", "Doppelgangland")
Wishverse Xander ("The Wish")
Zachary Kralik ("Helpless")

Wizards, witches, sorcerers and other magic users

Madam Anita ("Couplet")
Captain Atkinson ("The Thin Dead Line")
Helen Bointon ("Happy Anniversary")
Magnus Bryce ("Guise Will Be Guise")
Jenny Calendar
Cordelia Chase (through the former power Jasmine; notably in "Orpheus" and "Inside Out")
Command Central witches ("The Long Way Home" onwards)
Michael Czajak ("Gingerbread")
The Order of Dagon ("No Place Like Home")
The Devonshire Coven (mentioned in "Grave" and "Lessons")
Lucien Drake ("Soul Purpose")
Rupert Giles
Magnus Hainsley ("Just Rewards")
Clan Kalderash: Enyos Kalderash, Magda Kalderash (The Elder Woman)
Kumiko ("Wolves at the Gate, Parts 1-4")
Count Kurskov ("Waiting in the Wings")
Paul Lanier ("Guise Will Be Guise")
Jonathan Levinson
Allen Lloyd ("Sense & Sensitivity")
Tara Maclay
Catherine Madison ("Witch")
Amy Madison ("Witch")
Mistress Meerna ("A New World")
Gwendolyn Post ("Revelations")
Rack ("Wrecked", "Seeing Red", "Two to Go")
Ethan Rayne
Roden ("No Future For You, Parts 1-4")
Marcus Roscoe ("Carpe Noctem")
Willow Rosenberg
Professor Oliver Seidel ("Supersymmetry")
The Shadow-Men ("Get It Done")
Spanky ("Conviction")
Svear Priestesses ("Soulless")
Thelonious ("I, Robot... You, Jane")
Vaughne and the UC Sunnydale Wiccan Group ("The Killer in Me")
Andrew Wells
Wo-Pang of the Kung Sun Dai ("Awakening")
Wesley Wyndam-Pryce

Enhanced humans

Brain Man ("That Vision Thing")
Vanessa Brewer ("Blind Date")
Caleb
Bethany Chaulk ("Untouched")
Command Central psychics and seers ("The Long Way Home" onwards)
Connor
The Holy Triumvirate (The Three Blind Seer Children) ("Blind Date")
Mayor Richard Wilkins III
Ronald Meltzer ("I Fall to Pieces")
Cassie Newton ("Help")
Gwen Raiden
Marcie Ross and other Invisible Students ("Out of Mind, Out of Sight")
Slayers
Wolfram & Hart's Psychics ("Blind Date", "Quickening", "Hell Bound")
Wolfram & Hart's Telekinetic Ninja Assassin ("Quickening")

Dangerous mortals

Hunt Acrey ("Redefinition")
Richard Anderson ("Reptile Boy")
Ryan Anderson ("I've Got You Under My Skin")
Dr. Francis Angleman
Benny, Mr. Bryce's bodyguard ("Guise Will Be Guise")
Ilona Costa Bianchi ("The Girl in Question")
The Biker Gang ("Dad")
Billy's Kiddy League Coach ("Nightmares")
Congressman Nathan Blim ("Billy")
Brittany ("Harm's Way")
Gib Cain ("Phases")
Charlotte ("Harm's Way")
Mr. Chaulk ("Untouched")
Wilson Christopher and the Haxil's Cult Guys ("Expecting")
Jacob Crane ("Unleashed")
Cyril, W&H's mailboy ("Quickening")
Danny ("Harm's Way")
Debbie ("Salvage")
Lee DeMarco ("The House Always Wins")
Dick the Pimp ("Five by Five")
Lenny Edwards ("War Zone")
Elliot ("Ground State")
Emil the Arms Dealer ("Lineage")
Eric ("Some Assembly Required")
Bret Folger ("Five by Five")
Billy Fordham ("Lie to Me")
Frawley ("Homecoming")
Corbin Fries ("Conviction")
Frederick & Hans Gruenstalher and the Old Man ("Homecoming")
Gunn's ex-crew: Rondell, Gio ("That Old Gang of Mine")
Hank ("Parting Gifts")
Fritz Heinrich (SS officer) ("Why We Fight")
Henry, Deevak's human henchman ("First Impressions")
Captain Daniel Holtz
Holtz's Angel-hunters: Justine Cooper, Aubrey Jenkins
Jack the Barkeeper ("Beer Bad")
Jackson the Drug Dealer ("The Thin Dead Line")
Desmond Keel ("Conviction")
Knights of Byzantium: General Gregor, Orlando, Dante ("Checkpoint", "Blood Ties", "Spiral")
Knox
Irv Kraigle ("Dead End")
Lenny the Stalker ("In the Dark")
Rebecca Lowell ("Eternity")
The Lunch Lady ("Earshot")
Mac ("Parting Gifts")
Lindsey McDonald
The Maclay Family: Mr. Maclay, Donny and Beth ("Family")
Colonel McNamara
MacNamara Brothers: Darin and Jack ("The Ring")
Coach Carl Marin ("Go Fish")
Warren Mears
Lee Mercer
Dr. Michaels of Fairfield Clinic ("Dead End")
Lilah Morgan
Takeshi Morimoto ("Players")
Bob Munroe, Sunnydale Chief of Police
Linwood Murrow
Novac ("Just Rewards")
Gavin Park
Patrice of the Order of Teraka ("What's My Line, Part Two")
Preston ("Home")
Ramone, Lanier's mole in Caritas ("Guise Will Be Guise")
Nathan Reed ("Dead End")
Monsigneur Rivali & the Inquisitore ("Offspring")
Dr. Evan Royce ("Unleashed")
Ruddy ("Harm's Way")
Sam the Parole Officer ("Dead End")
Lacey Shepherd ("Home")
Fritz Siegel ("I, Robot... You, Jane")
Oliver Simon ("Eternity")
Rutherford Sirk ("Home")
Dr. Sparrow
Spencer, DeMarco's Head of Security ("The House Always Wins")
Sunnydale cops ("Empty Places")
The Faux T'ish Magev ("Guise Will Be Guise")
The Trio - Warren Mears, technology expert; Andrew Wells, summoner of demons; and Jonathan Levinson, caster of spells.
Tyke the Drug Dealer ("A New World")
Professor Maggie Walsh
Tom Warner ("Reptile Boy")
Tucker Wells ("The Prom")
Peter Wilder and the Avilas Cult ("Help")
Wolfram & Hart Security Guards: Howard ("Blind Date"), Phillip ("Blind Date"), Allan ("Dead End"), Dwight ("Blood Money")
Wolfram & Hart Special Ops Team: Commander Burke ("Quickening"), Agent Hauser ("Conviction"), Carlo ("Slouching Toward Bethlehem")

Undead

Adam
Francis Angleman ("Primeval")
Brian ("Provider")
Daryl Epps ("Some Assembly Required")
Forrest Gates ("Primeval")
The faux Ampata Gutierrez ("Inca Mummy Girl")
Josh ("Fear, Itself")
Holland Manners
Lilah Morgan
Jack O'Toole and his gang: Bob, Dickie and Parker ("The Zeppo")
Ovu Mobani zombies ("Dead Man's Party")
Prof. Maggie Walsh ("Primeval")
Wolfram & Hart Zombies ("Habeas Corpses")
Wolfram & Hart Failsafe Zombie Guards ("You're Welcome")
23rd Precinct Zombie Cops ("The Thin Dead Line")

Ghosts and spirits

The First Slayer
Hus and the Chumash Warrior Spirits ("Pangs")
Poltergeist/Ghostly Spirits of the Orphans' Emotions ("Where the Wild Things Are")
Grace Newman ("I Only Have Eyes for You")
Matthias Pavayne, the Reaper ("Hell Bound")
Pavayne's hell-sent Wolfram & Hart deceased employee apparitions ("Hell Bound")
Dennis Pearson ("Rm w/a Vu")
Maude Pearson ("Rm w/a Vu")
The Puma Guide ("Intervention")
Spirit Guides ("The Zeppo")
James Stanley ("I Only Have Eyes for You")
Tammy ("Birthday")
Talisman Spectres ("Lessons")
The Valet ("The Trial")
Wraith ("Spin the Bottle")
Wesley Wyndam-Pryce ("After the Fall")
Lowell House Ghosts ("Where the Wild Things Are")

Animalistic beings

Nina Ash
Buffy Summers (Beer Bad)
Peter Clarner ("Beauty and the Beasts")
Hyena people: Xander Harris, Kyle DuFours, Rhonda Kelley, Tor Hauer, Heidi Barrie, the zookeeper ("The Pack")
MacManus ("Unleashed")
The Neander-Guys: Colm, Kip, Hunt & Roy ("Beer Bad")
Oz
Veruca

Deities and higher beings

Beljoxa's Eye ("Showtime")
The Conduit to the Powers That Be ("Birthday")
Cordelia Chase (temporarily a higher power)
Dinza, Dark Demi-Goddess of the Lost ("Ground State")
First Evil
Glorificus, a.k.a. Glory
Hecate ("Bewitched, Bothered and Bewildered")
Jasmine
The Loa Alegba ("Loyalty")
Mesekthet's replacement (the White Room's Panther) ("Home", "Hell Bound", "A Hole in the World")
Osiris ("Bargaining, Part One)
The Powers That Be
The Ra-Tet: Mesektet, Manjet, Ashet, Semkhet and Ma'at ("Long Day's Journey")

Magical creations

Glory's Spawn of Sobek ("Shadow")
Jonathan's Augmentation Monster ("Superstar")
The Killer Clown ("Nightmares")
Olaf the Troll ("Triangle")
The Ugly Man ("Nightmares")
Willow's Dirt Golems ("Grave")
The Thaumogenesis Demon ("After Life")
Roden's golems ("No Future for You")
Dawn Summers

Monsters

The Bezoar ("Bad Eggs")
Bug monsters ("Fredless")
The 'Failsafe' ("You're Welcome")
Natalie French/She-Mantis ("Teacher's Pet")
The Lamprey Monster ("Doublemeat Palace")
Quor-Toth Sluks ("The Price")
Selminth Parasite ("Soul Purpose")
Sunnydale High Swim Team/Gill Monsters ("Go Fish")
Tentacle monster ("Sense & Sensitivity")

Robots

April ("I Was Made to Love You")
Ted Buchanan ("Ted")
Buffybot ("Intervention", "The Gift", "Bargaining, Part One", "Bargaining, Part Two")
Cyborg Cell ("Lineage")
Gwen, Wolfram & Hart's Files and Records ("Dad")
Mecha Dawn ("Wolves at the Gate")
Moloch the Corruptor ("I, Robot... You, Jane")
Warrenbot ("Villains")

Immortals and non-humans

Drogyn the Battlebrand
Eve, Child of the Senior Partners
The Guardian ("End of Days")
Marcus Hamilton, Child of the Senior Partners
The Immortal ("The Girl in Question")
The Oracles ("I Will Remember You")
The Shrouded Shaman ("Enemies")
Transuding Furies ("That Old Gang of Mine", "Offspring")
The Tribunal ("Judgment")
Wolfram & Hart's Prison Wardens: Zach, Trish, Ice-cream man, Mailman ("Underneath")