AD&D Hell Hound
A pack of big, angry firebreathing demon dogs is kind of self explanatory.
They are not explicitly demonic, but aren't from around here either. With good surprise chances, high HD, decent AC, and 1d10 bites that also deal an automatic fire damage equal to HD (4-7) with a save for half, they're threatening to both armored and unarmored people, and can locate hidden or invisible creatures 50% of the time. This is due to exceptional eyesight and hearing, rather than smell as you may have guessed, but honestly it makes sense they aren't bloodhounds if they've got fire shooting out their nostrils.
All in all, they fulfill much the same roll as other guard dogs, just on a higher 'power level.' The bandits have regular dogs, the goblins have wolves, presumably someone in the increased HD demihuman pool has wargs, the fire giants have hell hounds.
AD&D Herd Animal
Barely an entry and more of a suggestion that you can give animals 1-5 HD, a damaging attack, and a note that "Humans or humanoids of about man-size or less will be trampled to death if caught in the path of a stampede" which I have always thought sounded ripe for some rules-lawyer to buy a bunch of cattle and drive them before the party to trample Elminster or something.
They're big, they're tough, they're amphibious, they come in numbers, but there is not much else to say.
The classic horse with flippers and fish-tail hindquarters, that tritons often have. Did you know they apparently talk in their own language and can learn more, so you can have a talking fish horse? I didn't know that. They are also chaotic good because reasons.
Being half bird half horse as opposed to half bird half lion, Hippogriffs seem to me to be a much lamer sort of Griffon, and their statblock does little to disabuse me of this notion, essentially being half a griffon in HD and price of their young and eggs on the open market. They are slightly faster, and are omnivores, in comparison to carnivorous griffons and herbivorous pegasi.
Sunset Realm Hell Hound
The punishment for Bad Dogs (and humans) who repay kindness with viciousness, as prescribed by the Jackal God of Yuba, is to become a hell hound. Their sense of smell choked by smoke, their burning breath spoiling any attempt at kindly interaction, their spiritual existence is an exaggerated mirror of their violence in life, sicc'd on the enemies of Yuba. Those hell hounds who come to miss kindness and repent their own wickedness after a few years of this afterlife can be reborn as dogs or humans once again to try to do better next time, while those who revel in the hunt will forever be demons set to torment the enemies of Yuba, so their bloodthirst might at least be put to good use. Some slip their leashes and run rogue, at which point Very Good Dogs will be assigned to fetch the hellhounds soul back to the Jackal. As in life, they come in all breeds and sizes, but they are blackened by soot and ash and glow from the fires within.
Sunset Realm Hippogriff
Rather than an independent species, Hippogriffs are chimerae, artificial hybrids of bird and horse made by designer Beast Breeders and given a unifying name for marketing purposes (those purposes being a Griffon that can trot, mostly). Unlike Griffon-patterns, Hippogriffs did not escape and thrive in the wild and exist only as domestic populations, primarily in the Beast Islands and Mercia. They are seen as 'budget gryphons' and despite(or perhaps on account of) being considerably more affordable, they never became superbly popular among the nobility.
|From the medieval tome of 'things that didn't happen'|
In Mercia, a Hippogriff is a term used for a lower-class person who puts on airs in order to try to interact with the nobility as equals, as some nouveau riche would purchase Hippogriffs in order to keep up (literally and socially) with Gryphon-riding Mercian nobles. As many of these people were lowborn but successful military commanders who amassed Hippogriff squads as budget Gryphon-Knights and held considerable military power despite their lack of titles, and wanted recognition, there is an undertone to the word that insinuates a 'Hippogriff' is someone who might be dangerous to the status quo as well.
In the Beast Islands "Hippogriff" also has derogatory connotations, but in a different sense, indicating something is a cheap knockoff, a product with corners cut rather than a piece of art, etc etc, due to hippogriffs being just that with regards to Gryphons.
Like Gryphons, they were almost entirely phased out by Oroboron Gwyverns by the 6th age, as the value of flying mounts turned more towards speed and efficiency, as claws and fangs were eclipsed by firearms wielded by the rider.
Sunset Realm Hippocampus
Like Hippogriffs, Hippocampi are also artificial Chimera, but unlike the Hippogriffs, Hippocampi were created by the Ningen, the huge fish-people of the sea, as something to trade with land-dwellers-2nd age elves in particular. As such, Hippocampi have a bit of feyness to them compared to the monstrous wild gryphon or the domestic Hippogriff. While all animals can potentially speak, hippocampi had to keep up with the linguistic whimsy of elvish companions, and as such are quite clever in ways one would not expect, not to mention rather independent. They choose their riders and will not abide being tied to a dock-post like a donkey left outside the local inn, but if their independence is respected they can be loyal to humans, but more as a 'friend you visit and can give you a ride' than a beast of burden.
Ironically, the Ningen do not treat Hippocampi with the respect land-walkers afford these sea-steeds. The Ningen created the hippocampi as bargaining chips, steeds for landwalkers, but the Ningen, being larger by far and perfectly capable of swimming on their own, view Hippocampi as a fun species to hunt and prey upon, the taste of horseflesh without the bother of interacting with the land. As such, Hippocampi live in moderate terror of their own creators, which may explain some of their eagerness to ally with landwalkers.
Sunset Realm Hippopotamus
If ever there were any, they are surely gobbled up by now.