Nations Overview: Underwater
(R'lyeh, Atlantis, Oceania, Pelagia, Ys)
R'lyeh is central to much of the underwater factions lore, as DarkLight
mentioned, and we saw them foreshadowed at the end of threadmark
A Question of Origins. Space illithids with psychic powers arriving in a falling star at the start of the Middle Age, strong in Astral and Water magic, occasionally dabbling in Death and Earth. Start out underwater, but scary to everyone because their army is amphibious except for a few aquatic-only slaves. Illithids have a mind blast attack, which concretely means "Multiple-use LOS-range stun attack, magic resistance negates". Recruiting an illithid costs about 5x what a normal soldier does, so they're too costly to mass-produce, usually fronting enslaved mermen and underwater beasts.
It's easy to call R'lyeh "lovecraftian", but the Deep Ones are in
Atlantis. Much like our own Pale Ones, the Deep Ones never stop growing, their kings and queens are immense, they're strongly aligned to one path of magic (Water), and in the EA -> MA transition they lose some of their oldest native giants but pick up some human auxiliaries. Atlantean soldiers wield poisonous coral glaives and armor. Atlantean mages have a little Astral, Fire and Earth to back up their Water focus. Atlantean priests are powerful and zealous. Mostly amphibious.
Oceania reminds me of the jokes about D&D players who put multiple Half-X templates on one character. A mixed bag of half-fish mer-man versions of a bunch of creatures which were already half-human in Greek myth: mer-dryads, mer-harpies, mer-centaurs, mer-minotaurs, mer-satyrs. They use bronze weapons, partly because iron would rust and partly because their faction shtick is The Primitive Wild (But Underwater). Strongest in Nature magic, secondary Water, a little Earth on the mer-minotaurs and a little Air on the mer-harpies. One of the least changed nations as the Middle Age starts. Amphibious except for the mer-dryads.
Pelagia is run by twin-tailed Tritons, who are strictly aquatic. Since their best units can't go on land, this faction sucks in a regular game. They have some minion Mermen though. Their special stick is being able to convert Water into Astral magic resource at 1:1 instead of 2:1, hence the name of the Pearl Clan Tritons. Strongest at Water magic, sprinkled with Nature, Astral, Earth and Air. Units are several kinds of triton+merman infantry, some aquatic cavalry on healing mer-unicorns, and some mer-unicorns (hippocampi) without riders.
Ys used to be a land nation in the Early Age. Specifically, it's a splinter state of Tír na nÓg, which in the lore was mostly destroyed in the Age transition. The Tuatha sorceress Dahut hid the city of Ker-Ys beneath the waves to avoid the cataclysm, and it became the new capital of Ys. Many of her fellow sorceresses accompanied her, making Ys strongest in
Air magic and illusions and glamers, secondary Water and Earth, and a little Astral and Nature. The champions of Ys ride fire-breathing fey horses and kelpies, and their line troops are humanoid merrows. Entirely amphibious, perhaps even better on land, as they can still raise druids and cavalry in land provinces.
Previously in the Nations Overview series:
Ermor Cluster.