Monsters
We start with a short introduction. Some interesting quotes:
"Any creature that is not a player character is called a monster."
"The monsters in this section and their abilities are of the strength and type most commonly encountered. The DM may wish to make these monsters stronger or weaker to suit the needs of the campaign. When adjusting the strength of a monster, the DM must also adjust the other abilities, such as Armor Class, Move, Damage, and Saves so that they balance with the monster's adjusted hit dice."
"All non-human monsters have infravision (heat-sensing sight) and may "see" objects by their heat up to 60' away in the dark. .... Fire or large sources of heat tend to mess up infravision."
The rest of the section goes over each part of the stat block.
Armor Class - Monsters' AC is a based on both the toughness of the monster's skin and the monster's speed and dexterity. A while back on ENWorld I did a survey of monster ACs in Moldvay. The results were: monsters range from AC 9 to -2 (Gold Dragon). Green Slime can always be hit. The average monster AC is 5.4, the median AC is 3.5, and the mode is AC 6 with 22 monsters. Most monsters are in the range of AC 7-5.
Hit Dice -
Hit Dice determines a monster's level, which also determines what level it is typically on, which also affects how many appear. More on that in a later post. By my calculations (not counting +/-, the NPC party with variable HD, or normal bats and rats, which have 1 hp), Moldvay provides 138 monsters from 1/2 HD (giant centipede, killer bee, kobold, normal human, and sprite) to 14 HD (old gold dragons). The largest group, unsurprisingly, is clumped in HD 1 to HD 4, which account for 77 monsters out of the total. Level 9 and above is made up entirely of different sized dragons (which Moldvay says may vary +/- 3 HD depending on age and size). Average HD for the entire Monster section is 4.4 HD. Not counting dragon variations it's much closer to 3 HD. The mode is HD 1 and HD 2, both with 20 monsters each (HD 3 only has 19) . Broken down this way, it's easy to see just how well the Moldvay bestiary is put together. The majority of monsters are at the same level as the PCs, but there are still many monsters of higher HD for harder challenges and goals for further advancement.
Monsters that have special defenses are shadows and wights (only harmed by magical weapons), gargoyles (only harmed by magical weapon or spells), lycanthropes (only harmed by magical or silver weapons, or spells), yellow mold (only harmed by fire), green slime and ochre jellies (only harmed by fire or cold), gelatinous cubes (harmed by fire and weapons, but not cold or lightning), and gray oozes (harmed by weapons and lightning, but not fire or cold).
Move -
Most monsters move 120'/turn, and 40'/round. Some others are a bit slower at 90'/turn and 30'/round. By far the fastest ground moving monster is the panther, with an astounding 210'/turn, 70'/round. The only thing faster is a dragon in flight, with 240'/turn, 80'/round.
Attacks -
Out of 107 listed monsters, 24 have multiple attacks in a round. Moldvay also lists some special attacks: Poison, Paralysis, Energy drain, Charm, and Acid. Monsters using Poison include cave locusts, giant centipedes, killer bees, medusae (snake hair), rats (disease), snakes (except rock pythons), giant spiders, and troglodytes (stench can cause -2 to-hit). Monsters using Paralysis include giant bats, carrion crawlers, gelatinous cubes, ghouls, medusae (Turn to Stone), and thouls. Monsters using Energy Drain include wights (standard Energy Drain) and shadows (drains Strength for 8 turns). The harpy is the only monster that can Charm, barring spells. Acid using monsters include oil beetles, gray oozes, green slime (afte a fashion), and ochre jellies.
No. Appearing -
As mentioned above, this will change depending on whether a monster is at a dungeon level above, equal, or lower than its own level. However, the difference is largely left to the DM's discretion. Each monster has a standard number for a standard encounter, and another number in paranthesis for when encountered in the wilderness or in its lair. By far the most numerous is the normal bat, with 1-100 in the dungeon and 1-100 in the wilderness/lair. But aside from that, the most numerous in the dungeon is the normal rat with 5-50, and the cave locus with 2-20. The dungeon clean-up crew will only be 1, and only in dungeons, never in wilderness. The most numerous in the wilderness/lair, aside from bats, are goblins and orcs with 10-60. What's scary is dragons, I think typically thought of as solo creatures in most editions of D&D, have a No. Appearing of 1-4.
Saves -
Almost all monsters save as fighters. Of these, the highest is Fighter 11 (gold dragon), with most (65 out of 92) saving as Fighter 1, 2 or 3. Eight save as Normal Men, and seven save as Fighter 4. Only 2 save as Fighter 5 - the rock statue and the weretiger. Above Fighter 6 is mostly dragons, except for werebears (Fighter 6), gargoyles (Fighter 8) and the surprisingly tough doppleganger (Fighter 10!). The average monster save is Fighter 2.7, which is pretty much a wash, since fighters have the same saves from levels 1 to 3! In addition to these, acolytes, bandits, dwarves, elves, halflings, and mediums save as their perspective classes. Gnomes save as Dwarf 1, while pixies and sprites save as Elf 1. Saves generally follow HD, but not always. Moldvay actually provides a rule that is rather 4e-ish in retrospect: unintelligent monsters Save at 1/2 the level indicated by their HD, rounded up. The implication is that intelligent monsters save at the level of their HD, but even here you have some outliers. The doppleganger is a 4 HD monster with insane Saves of a fighter much higher in level. Likewise the Gargoyle.
Morale -
While morale can conceivably go from 2 to 12, the range in Moldvay is 5 to 12. The average is 8.5. Most fall under 8 or 7, with a good number at 9, and the 4th highest total being 12. Morale 12 includes the dungeon clean-up crew and all undead, but also lizard men, minotaurs, shadows, and shriekers. Beserkers and driver ants fight to the death once engaged in combat. The lowest morale monsters are normal rats and cave locusts at 5. Interestingly, dragons, while powerhouses in HD and Saves, only have merely good morale ranging from 8 to 10. Along with the rules for subduing, this reinforces the fluff of dragons being concerned with self-preservation before virtually all else.
Treasure Type -
This was a surprise. The most common treasure type, comprising nearly a quarter of all monsters, is...Nil. The next common type is U, which is an individual treasure type that has a small chance to provide nearly anything except electrum or platinum, followed by V, which has a small chance of anything except for copper. Dragons have H, which is by far the best, with good chances of gold, electrum, silver, and gems, and since it's a lair type, the coins number in the thousands. Only dragons have H.
Alignment -
The most common alignment is Neutral, with 66 monsters. Next is Chaotic, with 26. Lawful monsters number 7 (which includes dwarves and halflings). Finally 6 monsters may have Any alignment.
What is interesting to me when looking over these numbers is just how much treasure is not tied to monsters. I mean, the typical stereotype of D&D is hack-n-slash murderhoboing. Kill monsters, take their stuff. But the majority of monsters have little to no stuff! Nor does the basic bestiary especially call to mind B2, with dungeons filled with evil humanoids to kill and loot. The majority of monsters are unintelligent animals with no treasure. Almost certainly not worth fighting, if one can help it.
The examples of play do paint a different picture, but if I were to imagine a game based only on the monster list, I'd say that the point of Basic D&D would be to go into a dungeon and grab loose treasure in empty rooms while avoiding fantastic wildlife.