All The Monsters You'll Ever Need...

...are in these two rulesets, basically.

[EDIT: added the Wood Golem 24/09/2020]

These are not the only monsters you'll ever need. And I think animals (giant or normal) should get a pass. 

It's not new or big or clever to advocate reskinning and remixing, but these are the ones that really started jumping out at me when I reread my BECMI decades later. Something I like to do is splice one or more monsters and average out the stat-line (Croglin Vampire = (Thoul + Giant Shrew) x 0.5).

There's nothing poisonous, because venom is just so easy to add.

Honourable mentions are just ones that I like. 

From the BECMI Basic Set (all movement rates as % of Normal Human for your game):

• Bears
• this is very important - I'm referring to this and to this
• Bugbear AC +4, HD 3+1, Mv. 75%, Att. weapon +1 Hit & dmg, ML 9, surprise 1-3 on d6
• my mental reference is the hairy, shark-toothed, pumpkin-head, grinning giant goblin - but amongst other things, I also think -mechanically and thematically- it makes a much better Orc than the Orc

My first Bugbear (Citadel miniatures D&D Monsters set).
Not my paintjob; not my mini; not my picture.

• Ghoul 
• trick entry - almost anything on this initial list makes a pretty good Ghoul 
• Halfling AC +2, HD 1-1, Mv. 75%, Att. weapon, ML 7
• but don't play them as a stat-line, play them as classed NPCs with their full abilities; I'd also extend the AC bonus to vs. human-sized opponents
• Humans
• all the Humans you like; and say they're green and ugly and it's Lawful Good to kill them if that's what you want for your Orcs
• Pixie AC +6, HD 1, Mv. 75% Fly 150%, Att. weapon 1-4, ML 7, invisible - surprise you, then you're -4 to Hit them, rest every 4th turn when flying
• Shadow AC +2, HD 2+2, Mv. 75%, Att. touch 1-4 + 1 point STR drain (recover in 8 turns), ML 12, magic weapon to hit, surprise 1-5 on d6, immune to sleep, charm and Turning
• Shrew, Giant AC +5, HD 1, Mv. 150%, Att. 2 bites 1-6 each, ML 10, 60’ echo-location, always strike first then +1 Initiative, ferocious attack vs. 3HD or less - save vs. death ray or flee
• Thoul AC +3, HD 3, Mv. 100%, Att. 2 claws for 1-3/1-3 or 1 weapon, ML 10, paralysis touch, regenerate 1 hp/round
• Troglodyte AC +4, HD 2, Mv. 100%, Att. claw/claw/bite 1-4 ea., ML 9, chameleon 1-4 on d6 (surprise), stench - save vs. poison or -2 to Hit them in melee
• Wight AC +4, HD 3, Mv. 75%, Att. 1 level energy drain, ML 12, silver or magic weapon to hit, drained victims rise as Wights in 1-4 days, Undead
• Honourable Mentions: Normal Bats, Oil Beetles, Elf, Gelatinous Cube, Giant Locust, Lycanthropes, Ochre Jelly, Ogre, Owl Bear, Shrieker, Sprite, Giant Spiders, Stirge

From the BECMI Expert Set:

• Black Pudding AC +3, HD 10, Mv. 50%, Att. 1 for 3-24, ML 12, all but fire attacks cause it to split/multiply (2 HD Att. 1-8)
• could have gone with the Ochre Jelly, but the Pudding is somehow more iconic
• Golem, Wood AC +2, HD 2+2, Mv. 100%, Att. 1 for 1-8. ML 12, magic weapon to hit, -1 Initiative, -2 save vs. fire & +1 hit per damage die, immune to sleep, charm, hold, gas, cold and all missiles (inc. magic missile)
• in some ways, it's a better Mummy than the Mummy

Mummy from Dungeon Master.
Great game.

• Mummy AC +6, HD 5+1, Mv. 50%, Att. 1-12 + disease, ML 12, if you see one save vs. paralysis or paralysed with fear, its disease prevents magical healing and slows natural by 90%, you need to use fire, spells, magic weapons to hit, but only for half damage, Undead
• Troll AC +5, HD 6+3, Mv. 100%, Att. claw/claw/bite 1-6x2/1-10, ML 10 (8 vs. fire/acid), start regenerating 3 hp/round 3 rounds after taking damage, except from fire or acid damage
• and more below
• Honourable Mentions: Blink Dog, Devil Swine, Gorgon, Nixie, Treant

From the BECMI Companion Set:

• Gargantua  AC as original, HD original x8, Mv. original x2, Att. original x4 damage, ML 11
• insta-Great Old Ones using monsters on and off the list
• Spectral Hound AC +11, HD 5, Mv. 125%, Att. 1 for 2-12 + special (save vs. spells or fade away in 24 hours, dimension door to restore), ML 12, silver or magic weapon to hit, immune to fire and cold
• Honourable Mentions: Gremlin, Haunts, Phantoms, Rock/Cave Toad, Snow Ape, Spirits

No monsters from the Master set make it in, but it has a good section of stuff for augmenting your existing ones:

• Changing Monsters (p.7-8), basically you give a + or - 1 to 3 to your monster to make it tougher without having to go Gargantua on it, or weaker, in an easy to apply way (the mechanic works for Lasting Wounds, too); can also be a monster ability, for (say) Vampires drinking blood, or Dragonwarriors Ire Goblins/Bugbears (Book 4, Out of the Shadows, p. 101-102 - they 'puff up' when they go into a frenzy)
• Spellcasters (Non-Human), including Lycanthropes and Undead (p.21-22)
• Undead Lieges and Pawns (p. 22-23), rules if you needed them or for homebrewing a Necromancer class
• Honourable Mentions: Adaptor, Dinosaur (the way they're divided into broad categories, rather than an endless list in Linnaean), Brown Dragon, Drakes, Hags, Lycanthropes (Werebats, foxes and seals), Nightshades, Nuckalavee, Planar Spider

Master Monster List.

And, on top of that, the Master Set gives a quick round-up of monsters from modules, accessories and previous D&D versions (Monster List, Part 3: Other Monsters Acolyte to Zombie Minotaur, p.42-44). 

Because the information is restricted to name, source and stat-line, you have no pre-conceptions about monsters you don't recognise and automatically apply your own imagination to the spare details. Conjure with the stats for Bhut, Brain Collector, Dusanu, Nagpa, Sabreclaw, Sacrol, and Tabi (I did), then be slightly underwhelmed when you see the official version in the Creature Catalog years down the line.

2nd Edition AD&D Troll.

Jim Holloway's 2e Troll.
2e Troll is the best and most Troll.

Not the whole Troll (AC +6, HD 6+6, Mv. 100%, Att. claw/claw/bite for 5-8x2/5-12), but these two characteristics:

• due to their agility trolls can direct... three attacks at multiple opponents
• this feature is also found in the 1e Monster Manual, and I think it bears attention as it implies that multiple attack monsters can only target one victim - that's three potential kills a round, rather than a single overkill, which makes for a different kind of threat.
• any natural roll of 20 with an edged weapon severs one limb
• I had been convinced that this was standard for Trolls until I came off rpg hiatus and then couldn't find it - AFAIK, 2nd edition AD&D is the only time this was canon

So it's not from BECMI, which was where I was trying to stay, but I consider these to be narratively important for the Troll, and mechanically interesting for the stat-block when re-mixing/-skinning.

I don't think I've ever used a Troll as a Troll - it makes a surprisingly terrifying Vampire, though, and a fair approximation of The Thing (John Carpenter, obvs, but maybe suits the Howard Hawks one better).

Tunnels & Trolls.

T&T 5e polishes off monsters in 2-3 pages (there are supplements later). Ken St. Andre writes:

What lurks and slithers in your imagination I don't know, but in mine there are fire-breathing dragons, crocodiles, unicorns, snarks, sharks and boojums, black hobbits, giant spiders, cave lions, pythons, centaurs, toothy non-flaming dragons, wyverns, wurms, griffins, hippogriffs, werewolves and vampires, balrogs, basilisks, ghosts, jubjub birds, slithy toves, cave bears, sphinx, enchanted warriors, zombies, reptile men, flame fiends, harpies, orcs, ogres, gremlins, goblins, trolls, giants, two-headed giants, three-headed giants, mushroom monsters, cockatrices, giant slugs, banshees, mummies, barrow-wights, living statues, shoggoths, wraiths, demons, leopards, octopi (giant economy size), gnloes, minotaurs, slime mutants, drooling maniacs, half-orcs, hydrae, living skeletons, bandersnatchi, jabberwocks, pithecanthropi, ghouls, mad dogs, poisonous vipers, blood rats, night gaunts, lamiae, cannibals, witches, warlocks, rabid rats (ulsios), chimerae, hags, giant slimy worms, yeti, tigers, gorgons, bigfoots, invisible stalkers, were-creatures of all varieties, misanthropes and misogynists, manticores and lots more.

Then there's a Monster Rating to dice & adds chart, and a monster selection with MRs and No. App. based on level, and that's it.

My first question -after 'is gnloes a typo?'- was 'but how do I know what a ghoul does?' Which was the wrong question, because I know what a ghoul does and, anyway, isn't it me that gets to decide what a ghoul does, isn't it my game now?

Reginald Scot & Michael Aislabie Denham.

St. Andre's monster jam has the same kind of energy (possibly deliberately) as this from Scot's Discoverie of Witchcraft:

​...they have so fraied us with bull beggers, spirits, witches, urchens, elves, hags, fairies, satyrs, pans, faunes, sylens, kit with the cansticke, tritons, centaurs, dwarfes, giants, imps, calcars, conjurors, nymphes, changlings, Incubus, Robin good-fellowe, the spoorne, the mare, the man in the oke, the hell waine, the firedrake, the puckle, Tom thombe, hob gobblin, Tom tumbler, boneles, and other such bugs, that we are afraid of our owne shadows.

...and this, from the 19th Century Denham Tracts, which takes Scot as its foundation:

"…the whole earth was so overrun with ghosts, boggles, Bloody Bones, spirits, demons, ignis fatui, brownies, bugbears, black dogs, spectres, shellycoats, scarecrows, witches, wizards, barguests, Robin-Goodfellows, hags, night-bats, scrags, breaknecks, fantasms, hobgoblins, hobhoulards, boggy-boes, dobbies, hob-thrusts, fetches, kelpies, warlocks, mock-beggars, mum-pokers, Jemmy-burties, urchins, satyrs, pans, fauns, sirens, tritons, centaurs, calcars, nymphs, imps, incubuses, spoorns, men-in-the-oak, hell-wains, fire-drakes, kit-a-can-sticks, Tom-tumblers, melch-dicks, larrs, kitty-witches, hobby-lanthorns, Dick-a-Tuesdays, Elf-fires, Gyl-burnt-tales, knockers, elves, rawheads, Meg-with-the-wads, old-shocks, ouphs, pad-foots, pixies, pictrees, giants, dwarfs, Tom-pokers, tutgots, snapdragons, sprets, spunks, conjurers, thurses, spurns, tantarrabobs, swaithes, tints, tod-lowries, Jack-in-the-Wads, mormos, changelings, redcaps, yeth-hounds, colt-pixies, Tom-thumbs, black-bugs, boggarts, scar-bugs, shag-foals, hodge-pochers, hob-thrushes, bugs, bull-beggars, bygorns, bolls, caddies, bomen, brags, wraiths, waffs, flay-boggarts, fiends, gallytrots, imps, gytrashes, patches, hob-and-lanthorns, gringes, boguests, bonelesses, Peg-powlers, pucks, fays, kidnappers, gallybeggars, hudskins, nickers, madcaps, trolls, robinets, friars' lanthorns, silkies, cauld-lads, death-hearses, goblins, hob-headlesses, bugaboos, kows, or cowes, nickies, nacks, waiths, miffies, buckies, ghouls, sylphs, guests, swarths, freiths, freits, gy-carlins, pigmies, chittifaces, nixies, Jinny-burnt-tails, dudmen, hell-hounds, dopple-gangers, boggleboes, bogies, redmen, portunes, grants, hobbits, hobgoblins, brown-men, cowies, dunnies, wirrikows, alholdes, mannikins, follets, korreds, lubberkins, cluricauns, kobolds, leprechauns, kors, mares, korreds, puckles, korigans, sylvans, succubuses, blackmen, shadows, banshees, lian-hanshees, clabbernappers, Gabriel-hounds, mawkins, doubles, corpse lights or candles, scrats, mahounds, trows, gnomes, sprites, fates, fiends, sibyls, nicknevins, whitewomen, fairies, thrummy-caps, cutties, and nisses, and apparitions of every shape, make, form, fashion, kind and description, that there was not a village in England that had not its own peculiar ghost.

Don't you just want to know what they are and what they're up to?

For some definition/speculation, follow this link.

Also, there're hobbits right next to hobgoblins, some time in the mid-1800s, plus some comeback to those who say that there's too many monsters (including me).

P.S. #BOSR

Dragon magazine #158.

Yet another object I regret giving up.

Ethan Ham's article 'Also Known As... The Orc' gave variations on many standard monsters by collecting differing names from fiction, history and cultural diversity.

Monsters reduced to basic stat-lines only need a name to bring them to new life.

If the villagers say they're being attack by Fomorians or Land-Wights or Trolls, you've got different expectations than if they say they're being attacked by the Orcs that have recently taken over the abandoned burial mounds. And you've got a reason to make them 'not just Orcs again', too.