Ochre Jelly: Ochre Jellies first appeared in OD&D Vol. 2. Their Hit Dice has increased from 5 to 6, and they now appear in groups of 1-3 instead of always being solitary. The damage they do has changed very slightly, from 2-12 to 3-12. The ochre jelly is an unusual case, in that it seems to have been simplified from OD&D to AD&D. The basic monster is still the same, a giant amoeba that seeps through dungeons. They are still split into two smaller jellies by lightning attacks, but in OD&D attacks from weapons did the same thing. There’s no mention of that here. (As a side note, these smaller jellies are now said to do half normal damage.) There’s also nothing mentioned in AD&D about them being unable to eat through metal or stone, nor that they can dissolve wood (although they do eat cellulose, which I suppose could be stretched to include wood eating). The only new ability it gets is that it can travel on the walls and ceiling.
Octopus, Giant: Originally included as a rumoured monster in OD&D Vol. 3, giant octopi first got stats in Supplement II: Blackmoor. Their Number Appearing has decreased from 1-4 to 1-3. Their swim speed has increased from 9 to 12. And their Hit Dice has doubled, from 4 to 8: obviously the average octopus now encountered is much bigger than before. Even so, their tentacles do less damage, from 1-6 down to 1-4, but their bite has gone from 1-6 to 2-12. It has gained the ability to constrict foes, which it couldn’t do before, and there are a whole host of rules about arms being pinned and how strong you need to be to stop from getting crushed. Another big change is that they now have an alignment of Neutral (Evil), which makes them just that little bit more sinister.
Ogre: Ogres debuted in OD&D Vol. 2. Their Number Appearing has changed slightly, from 3-18 to 2-20. Otherwise their stats are the same, but their description has been substantially filled out. They now have leaders like the other humanoid races. They get bonuses to hit and damage if using weapons. They have females and young in their lairs, and they also keep slaves. (But they like to eat the demi-humans, so there’s not much chance you’ll find any dwarves, elves or halflings as ogre slaves.) They have their own language, and can also speak Troll and Stone Giant. They mingle with trolls and giants a fair bit, and are sometimes enslaved by demons. They get a physical description (big, ugly and mostly yellow-skinned) and their lifespan is at least 90 years. The biggest change is that they no longer carry as much treasure as they once did. A wandering ogre in OD&D could be counted on to be carrying from 100 to 600 gold pieces, but now the average one only has 20 to 80 gp. It makes sense with the law of diminishing returns, I guess.
Ogre Mage: This monster first appeared in Supplement I: Greyhawk. Statistically, it hasn’t changed at all. Surprisingly, they’re still extensively referred to here as Japanese Ogres. I thought that would have been gotten rid of by now, but I do think it’s inclusion is an important pointer towards the mythological source of the creature. They still have the same boatload of special abilities: invisibility, fly, cause darkness, polymorph into a human form (now with a limit on allowable height), charm person, sleep, cone of cold (which now does 8d8 damage instead of 8d6), and regeneration of 1 hit point per round. The regeneration has also been altered to allow the creature to reattach severed limbs. They also get the new ability to assume gaseous form, as if they weren’t slippery enough. The only other additions to their entry are that they have 9 Hit Dice leaders, and that they get a physical description.
Orcs: Orcs (of course) first appeared in OD&D Vol. 2. The only statistical change made to them is that their basic damage has increased from 1-6 to 1-8. Orcs of different tribes are still hostile to each other, but slightly less so: there is a 75% chance of leaderless tribes attacking each other, rather than it being automatic. There’s a list here of known orc tribes, with names like Vile Rune and Leprous Hand, and those will definitely be going into my campaign. In OD&D orcs always had high-level NPC fighters or magic-users as leaders, but now there are tougher orc leaders to do the job. The only other monster you might now encounter in an orc lair are ogres, which is a big step down from the possibility of trolls or dragons in OD&D. Orcs encountered outside their lair still have a chance to be escorting a wagon train loaded with treasure, but the treasures therein will be much less generous. To balance that out, they will now have slaves. Like the other D&D humanoids, orcs now explicitly have females and young. Their weapons are outlined (a varied selection), they can carry a standard that makes them fight better, and they get a physical description.
Probably the biggest addition here is the half-orc. Half-orcs were first mentioned in an article on Birth Tables in #3, but only in passing. It’s here that they are detailed for the first time. Surprisingly, the entry doesn’t just talk about orc-human hybrids, but also orc-goblins and orc-hobgoblins. The idea is that orcs will breed with anything, so I wouldn’t restrict it to those three. The only combination specifically ruled out is elves and orcs.
Giant Otter: Giant Otters first appeared in Supplement II: Blackmoor. They’ve been given a complete overhaul. Number Appearing has decreased from 10-40 to 2-5. Armor Class has improved from 6 to 5. They’ve gained a swim speed of 18”. Hit Dice has increased from 3 to 5. Their bite damage is still a whopping 3-18, but they no longer get claw attacks. Gary has a tendency to demystify the monsters that are basically Earth animals, and he does it again here. In Supplement II giant otters had a “vast native intelligence” that prevents them from falling into traps, but it’s not mentioned here. Nor is the possibility of domesticating them. But in true Gygax form, he does give an exact value for their pelts.
Otyugh: The otyugh makes its debut here. It’s a large monster with ridged tentacles and a huge mouth that lives underground and eats dung and offal. Their primary ability is that their bite will transmit disease 90% of the time. It’s not said if there is a saving throw to avoid this, but I would say not. The disease is specified as typhus, though no further details are given. Typhus was detailed in Supplement II, where it gave a 25% chance of death, and a chance that any survivor will have a relapse every 5 years. I expect that this will be further expanded on in the Dungeon Masters Guide. Probably the most interesting thing about the otyugh is that it often lives in symbiosis with another monster, scavenging droppings and carrion. I just think it’s a shame that they’re so often solitary; having one mid-level monster following something more powerful around seems like a waste, but a whole horde of these suckers living in the bowels of a dragon cave would be cool.
Giant Owl: As far as I can tell, giant owls have only appeared in the wilderness encounter tables from Supplement III: Eldritch Wizardry. They get stats here for the first time, and with 4 hit dice they’re pretty butch. Their main ability is that they have a 5-in-6 chance to gain surprise. They’re also very intelligent and can speak their own language. They are said to sometimes befriend other creatures, but nothing is said about the circumstances this might happen in. And as usual, their young and their eggs get the patented Gygax monetary value.
Owlbear: Owlbears first appeared in Supplement I: Greyhawk. The only statistical change is that they have 5+2 hit dice instead of 5, and there are no other changes in the description either. They still get a bear hug attack if they roll an 18 or better on a claw, and the rest of the description is just a fleshing out of what was already in OD&D. It is postulated that they are “probably the result of genetic experimentation by some insane wizard”. And of course their young and their eggs are given a market value. (Does anyone else find it weird that owlbears lay eggs?)