13,394 NPCs

Classic reference; current Forever availability is unconfirmed.

NPCLevelTitleZone
Polymorph Clone10Azshara
Lieutenant Nevell1The Argent DawnDun Morogh
Lieutenant Lisande1The Argent DawnThunder Bluff
Lieutenant Dagel1The Argent DawnOrgrimmar
Lieutenant Rukag10The Argent DawnUndercity
Lieutenant Beitha1The Argent DawnDarnassus
Naxxramas Follower61Naxxramas
Naxxramas Worshipper61Naxxramas
Faint Necrotic Crystal60
Garon Hutchins60Silithus
Crypt Guard61Naxxramas
Blackwing Spell Marker1Blackwing Lair
Midsummer Celebrant2–4Stonetalon Mountains
Plague Slime (Blue)61
Plague Slime (Red)61
Plague Slime (Green)61
Argent Quartermaster1The Argent DawnIronforge
Argent Outfitter1The Argent DawnUndercity
Festival Flamekeeper60Orgrimmar
Deathknight Understudy60Naxxramas
Festival Loremaster60Teldrassil
Festival Talespinner60Thunder Bluff
Death Lord61Naxxramas
The Lich King60Naxxramas
Mouth of Kel'Thuzad1–60Ironforge
Mr. Bigglesworth5Naxxramas
Stormwind Firebreather23–33Stormwind City
Orgrimmar Fireeater59–60Orgrimmar
Ironforge Firebreather23–33Ironforge
Darnassus Firebreather23–33Teldrassil
Thunder Bluff Fireeater59–60Thunder Bluff
Undercity Fireeater59–60Undercity
Ribbon Pole Debug Target1Ironforge
Chief Expeditionary Requisitioner Enkles55Silithus
Emmisary Whitebeard55Eastern Plaguelands
Apothecary Quinard55Silithus
Emmisary Gormok55Eastern Plaguelands
Cenarion Scout1Silithus
General Kirika60Silithus
Marshal Bluewall60Silithus

Classic reference data from QuestieDB (Forever data, commit c5de61a), with positions on Forever's zone maps. It doesn't confirm that an NPC, location, quest or item is in Forever.