While inexplicably garbed in samurai armor in the illustration, hobgoblins do not have any actual correspondence to japanese mythology that I am aware of. Instead, they seem to be the D&D variant of the Uruk-Hai from lord of the rings, being superior to goblins in terms of being able to fight in sunlight or darkness, as well as having many siege engines in their lairs. Contrary to what you might expect given the general increase in depiction of orcs as the beefiest demihuman, hobgoblins are actually more powerful and larger than orcs, which is what makes me think they may have originally been Uruk-Hai with the name filed off, much as halflings were once hobbits.
Of some note is Koalinths, marine hobgoblins with gills. I do wonder at the fairly pointless oceanic palette swaps of some monsters, when ocean-specific entities liek Kuo-toa and Sahuagin fill that niche with more flavor for sure.
Compared to the other forms of artificial servitor in AD&D, which often require Limited Wish, these little creatures are quite reasonable to manufacture, requiring a hired alchemist, Mending, Mirror Image, and Wizard Eye, 1 pint of the casters blood, 500-2000GP, and 1d4 weeks. For a creature with 2HD, a sleep-causing bite, flight, and a telepathic link, that's a pretty good deal, apart from the 2d10 feedback damage sustained if it dies.
They are rather similar to Imps in the form of a diminutive, flying, and poisonous mini-me, but without the demonic traits. They seem a flavor monster above all else, a way to spice up NPC wizards, but I do wonder if they were ever commonly manufactured by players.
A horse is a horse, of course of course. But there are some horse-mechanics that may have been lost over the years- firstly, horses are said to panic 90% of the time when confronted with... well, basically any adventuring hazard, really. Warhorses panic only 10% of the time, and do not fight on the first round of melee, kicking and biting only on round 2 and beyond.
Tactically, a pretty good monster in that you can take its heads off rather than just abstractly attack its HP bar. Only 4 heads can gang up on a target at once, making them reasonably 'fair' to engage in melee with. Most do not actually regrow heads, which is fine in my book as everyone has seen Hercules, so the task to burn the stumps is less of a puzzle and more tedious busywork at this point.
Pyro and Cryohydra are of course more dangerous, having miniature breath weapons that can bypass armor and attack HP via saving throws instead.
AD&D Hyena- 3HD dog, with 5HD prehistoric version. Though interesting animals in real life, there's not much going for them in the game world.
Sunset Realm Hobgoblin-
Hob is merely a prefix meaning house, so a 'House goblin' is a goblin ready to serve as a house servant for their alvish masters, having been granted a name and a shadow to distinguish them from the nameless, interchangeable hordes of shadow-goblins servants. As time marched on and the shadowy-type died out without alves to replace them, basically all goblins became Hobgoblins, people rather than monsters, so the term became pointless and they were just referred to as goblins. Refer to the goblin-post for more details.
Sunset Realm Homunculus
Artificial children of biomancy and/or alchemy, Homunculi are traditionally grown in glass jars. They appear as a mixture of whatever blood was offered in their creation. While Chimerae may be grown via similar methods, Homunculi refers to creations that have human blood, even if their appearance does not end up humanoid. They are sometimes made as noble heirs, and may be referred to as 'clones' if grown from only a single donor's blood.
Notable historical/fictional homunculi include
-Barnabas O'Jar, companion to Queen Astrid of Del'Narith on her early adventures, including the chaining of Anathemant, later court sage and librarian. A homunculus grown by a wizard of a lost age who left Barnabas in a jar for years until the Queen and her companions rescued him.
-Seven-Veils, a toadlike little magical prodigy who made a pact with the Great Raven, threatened and saved Fassulia from the Forbidden Moon Gate, defeated Finzu the Egregrious during the Eclipse, and became the lead of the Tower of Cul'Khuwa in Phavea after a long and lawful history of defending the peace.
Sunset Realm Horse- Two gods compete over claiming responsibility for the domestication of the horse- the Horse-God of Yuba, and Our Lady of Gardens. While the Horse-God had a stronger claim in the 3rd and 4th ages, on account of having a horse's head, Our Lady's story became more popular in the 5th age onward, due to the death of the Horse God in the 4th intersolar period. Either way, horses are as part of human society as dogs, being a workforce, mode of transportation, and companion all in one.
Sunset Realm Hydra- A stolen idea I got from one of my players is Hydra-as-template to apply to anything whose heads or limbs are notable. This is a jolly good idea, and so the Sunset Realms has Hydraitis, a rare disease that causes ravenous hunger to fuel regeneration and replication of heads, limbs, or both. It most commonly affects snakes and lizards on the Fault, that being the homeland of the disease spirit, but captured Hydra have spread the disease across the world.
The source of Hydraitis is an ancient gene-modding retrovirus from the days of Yg and the Serpent Empire, originally meant for the creation of medusa, but persisting in a fragmented, free-roaming form due to the various magical catastrophes wrought by wielders of the Orb of Omnipotence. This is why most hydra are reptilian (reptiles save with disadvantage against contracting hydraitis). Eating hydra flesh or blood forces a save vs poison/disease, and it is a potential result of the Death and Dismemberment chart if forced to roll upon it by an infected creature. New heads will retain about half the memories of the original, and so those afflicted become increasingly bestial and instinct-driven until they become a monster eating constantly to sate each head's hunger.
Sunset Realm Hyena
Also known as 'False Dogs' these animals dwell in the north deserts of the Fault and the deserts of Saresare. Cats and Dogs view them with unease, and although they rarely attack humans, (and can be distracted by jokes if they do) they are dangerous vectors of the grinning-plague, ghul fever, or whatever you want to call it, so are regarded as dirty menaces to society and are driven into the wilderness by most human societies. Some lion prides have hyena jesters, though such jesters typically are there as prisoners, rather than by choice, and would happily join anyone who could rescue them, at least until an opportunity to rejoin their own society presents itself.
In the 4th age, they were used extensively by the Korozong, that demon-cult of ghuls, and so it is not unheard of of -zong societies to still use them in the role of dogs, though that is mostly the domain of criminals and people overcompensating for something.
In Saresare, they have a friendly rivalry with Vulch with regards to fighting over corpses, and due to the ancient antics of the head-swapping Ibn Haur, saresaren society has a fair few hyena-headed folk known as Gnolls.