Not real sure how Saga Age of Magic works rule wise (and only the faintest idea of how Saga works) but I am always up for spitballing exotic fantasy army ideas, so going to anyways.(edit and its a long list)

A Medieval/Renaissance  Philippians army with fantasy touches would be interesting and pretty wild given their folklore.

Eastern European or straight up Medieval/Renaissance Russian fantasy army could have a lot going for it,  and would probably be easy to do with Saga.

I am surprised you didn’t add anything from the African content, does Age of Magic  have detailed army that covers things like Zulus?

A Persian empire with  Mythric/Zoroastrian mythic touches  themed army would be pretty easy to do, since their are 2 plastic lines out for Persians right now in 28mm.

Oh, and then there is generic sea dwellers like fish men  (don’t know what they would proxy as or if they already have an official list in AoM).

Also a few lot of details or branching options for one of your suggestions

For Korean dokkaebi, you could probably take some bareheaded elf models (something dressed like GW WFB high and dark elves or similar) or human models that look like they could pass as Korean (Fireforge’s mongol infantry) and just add horns or a horn to their foreheads, maybe throw in a loin cloth and club oni model, and play them as something archery and spear heavy.

One could do a pure Chinese themed army, particularly once Wargames Atlantic releases their Warring states and Boxer sets but you could do Terracotta warriors, Wuxi, undead, etc. themes right now if you can get your hands on some of the right Watchful I Studio or other mini makers products (and there are some STLs flouting around too). (P.S.: What 3 Kingdoms minis was Gerry talking about/showing off?)

Same deal, if not more so with Japanese historic and folklore themes, you have a lot more army style ideas to draw from again instead of just the typical Japanese human/yokai army theme, you could do Japanese themed Ogres, Undead, Goblins, Orcs, Dwarf, elves,etc. army lists subbing in yokai critters for the the normal models from foot soldiers to war beasts in said lists (if there are any such lists in AoM since I have no clue, but rule does apple to other rulesets like KoW and Oathmark). One can even drag in mythic characters as Leader/warlord/heroes  for some of these armies. Here are a few that would be my picks for leaders/heroes:

For an ogre themed list you have the oni and myth wise  you have these guys as leader/hero/warlord theme options for them:

Ōtakemaru: This brute could be a fairly basic oni model, or you could use an undead oni model for his later transformation  (and yes there are miniature options for that on the market).

Shuten dōji : An oni model with a big saki bottle and buddhist pray beads would probably do the trick for this fellow, if he is in the middle of drinking bonus points.

Kidōmaru: Shuten’s bastard son in the myths, I would use a Cow skull instead of a full cow disguise on an oni model.

Ibaraki dōji : Shuten’s lieutenant and in some myths, mostly where Ibaraki is female, his lover.  Again you could use any oni model but I would go the female oni or kijo route and probably use ether the reaper model or, if I want to be a little risque (since she is a  very bad girl you might), a certain Soda Pop miniatures’ Relic Knight’s model for her.

There are several undead army themes one could go with from the Japanese myths, but for the wasabi version of the classic skeleton army I recommend these  2 characters and this monster as must haves:

Taira no Masakado: Basically either a human samurai or a flouting head (not hard to do), I would use a flashy model that looks good painted if I where to do the human, head route box of samurai heads, taken care of , just add paint.

Takiyasha hime: Taira no Masakado’s avenging daughter  and a powerful necromancer with a fondness for frogs in Japanese myth, probably she normally depicted as riding around on a giant frog which might be a good project, but  if you want her for lore theme purposes could also just add some  head candles to geisha model or better yet suitably dressed female magic user model.

Gashadokuro: a giant skeleton monster Takiyasha hime summoned, more of a big monster unite but I added him cause he is related to the other 2. There are a couple of options for this out on the market one could use or convert to use for this easily (Zenit miniatures has one for kensi I believe and Reaper still has their giant Skeleton which is begging for this).

Sea dwellers are a pretty big thing in Japanese myth, and most obey the Sea Dragon Emperor/King  Ryūgū-jō (I have no article for him which is why his name is not blue). For a basic army theme I  would use mostly samurai and ashigura human models (maybe a fishy head swaps here or there) with some full fishmen thrown in all with bows and spears  and a big sea monster (recommend a shark, but one could also have a dragon) and play them as elves (again I don’t know how Saga AoM works), for Ryūgū-jō himself either the monster model (dragon form) or  some sorta of human sized character mini would do, maybe a dragon man in samurai apparel would be best if you can find one.

For most other forces again a lot you could do, but  for yokai in general I recommend going with a list that allows you to make a full on 100 demon night parade,  and at the head of that as a warlord you are probably going to want a Nurarihyon  who is the leader of all the Yokai. A decent warlike Nurarihyon  mini could probably be made simply by adding some green stuff to the back of the head of one of those “western goblins in Samurai cosplay” that keep getting made and sold as bakemo and yokai (they are not that). You might also want to add in Yuki onna as a spell caster/hero, and again not that hard to add since she can be done as a blue and white paint job to any  female mini with some frost/snow elements added, you could even go more “girl power” and use a female samurai or ninja instead of the traditional kimono wearing one.

Decided to look up what the factions/play styles where for AoM and found the  blackshawgaming and Harold’s Revenge blogs, so now I  have a mildly better idea what you are going for based on the names and what they where doing army wise (‘The Otherworld’ (demons), ‘Masters of the Underearth’, ‘The Horde’, ‘The Lords of the Wild’, ‘The Undead Legions’ and ‘The Great Kingdoms’ (medieval society)).

Yeah, I meant  Philippines as in the Filipino, Moro,etc. in the Archipelagos. Very colorful area historically, I think Old Glory has stuff for the early Spanish incursions/colonization of the area if you want to do ‘Great Kingdoms’. From what little I know about their folklore monsters, if one can get the models for it  you  might be able to do ‘The Otherworld’, ‘The Undead Legions’, and ‘The Lords of the Wild’.

There is actually a little history of armor Africa, admittedly mostly in the North, but there are some uniquely African examples.  Perhaps the most well know being from Southern Nigeria region in the form of the Benin Empire, and there are some 3D print greenskin minis based of  them.

If I where doing an Eastern European themed fantasy army for AoM, personally I would focus on Russia folklore and either do Vladimir’s knights of the Golden Table or Marya Morevna themed ‘Great Kingdoms’ with force which would be easy, though you could also probably do a ‘The Horde’ force for some of the baddies at least (maybe even goodies).

After finding out what the “factions” where, while you are right about the oni,  to be honest  ‘The Undead Legions’ and ‘Great Kingdoms’ (humans) would probably be the easiest and fastest ones to do out of Japanese folk lore with whats available  mini wise on the market right now.

Also given the sandbox like quality of them all, while ‘The Otherworld’ makes the most sense description wise for yokai in general, you could probably field a Night Parade themed force as any of the 6 mentioned pretty easily except maybe (and that’s a big maybe) ‘Masters of the Underearth’ and still make sense theme and playwise since yokai very in myth from being horror monster to parodies of feudal life (sometimes with the same monsters). Likewise a lot of forces from Japanese myths are pretty much just parallels the humanity, the Sea Dragon Emperor’s legions for example would probably work best with a ‘Great Kingdoms’ list.   If one has sculpting talent,  Yokai.com  likely has something one could use as inspiration to fill in that “punch/needed” unite on the roster

“fell down a rabbit hole” Dude, you dived in there, head first, knowing very well: “It’s a calculated risk but boy am I bad at maths” 😉

Ninja Donkeys is what you need

I bought Saga Age of Magic a couple of years ago and although I haven’t actually started anything yet, my intention was to build warbands themed on the factions in the Elderscrolls series of games.  I think you can actually do a relatively good job of building most factions using historical miniatures in “true” 28mm scale.  And with many manufacturers of historical miniatures also producing fantasy ranges alongside their historical ranges, you can even make some of the non-human races.  The only faction I can’t currently find any solid miniatures range for would be the khajeet cat people.  Cat people miniatures do exist but they never seem to capture the essence of the Elder Scrolls.

As a system I think it has so much potential because of the sheer flexibility that having no fixed factions gives you.