Spreadsheet update: just discovered that there are more 0e core monsters I missed, in Book III! More details in
the other thread.
Notably, this changes the answer in
post 106. In fact, looking at it again, I think I must have messed something up, because "every monster that was core in 1e + 2e + 3e + 5e" - which is what
@Parmandur basically asked for - is actually a total of 155 monsters:
Ankheg, baboon, badger, basilisk, black bear, brown bear, fire beetle, beholder, blink dog, boar, buffalo, bugbear, bulette, camel, carrion crawler, centaur, giant centipede, chimera, cockatrice, couatl, crocodile, giant crocodile, displacer beast, dog (mastiff), doppelganger, dragon turtle, black/blue/green/red/white dragon, brass/bronze/copper/gold/silver dragon, dryad, giant eagle, air/earth/fire/water elemental, elephant, ettin, gargoyle, gelatinous cube, djinn, efreet, ghost, ghoul, ghast, cloud/fire/frost/hill/stone/storm giant, gnoll, goblin, clay/flesh/iron/stone golem, gorgon, griffon, sea hag, harpy, hell hound, hippogriff, hobgoblin, homunculus, hydra, imp, invisible stalker, jackal, jaguar, kobold, lamia, lich, lion, lizardfolk, mammoth, manticore, medusa, merfolk, mimic, mind flayer, minotaur, mule, mummy, guardian naga, spirit naga, ochre jelly, giant octopus, ogre, oni, gray ooze, orc, otyugh, giant owl, owlbear, pegasus, phase spider, pixie, pony, pseudodragon, black pudding, purple worm, quasit, rakshasa, remorhaz, roc, roper, rust monster, sahuagin, salamander, satyr, giant scorpion, shadow, shambling mound, shark, giant shark, shrieker, skeleton, giant constrictor snake, giant poisonous snake, specter, androsphinx, gynosphinx, giant spider, stirge, tiger, treant, troglodyte, troll, umber hulk, unicorn, vampire, violet fungus, giant wasp, werebear, wereboar, wererat, weretiger, werewolf, wight, will o'wisp, wolf, dire wolf, winter wolf, worg, wraith, wyvern, xorn, zombie.
Worth comparing to
@overgeeked's
list of 179.