[HoneyBadger]

Couple of ideas-hopefully funny, as opposed to over-powered:

'Land of the Blind'
Plains province: This consists of 12 cyclopes, each equipped with one of the 'Eye' artifacts (so they're blind), and a Hammer of the Mountains. They're led by another cyclops modified to wear a crown, to have 100% Darkvision, and to cast 'Darkness' at the beginning of battle.

2 'Grave of the Ancestors': This is a mountain province containing a single giant head Pretender (as per Mictlan-I forget their names). The giant head Pretender is modified with a Secondform, so that if it's destroyed, it turns into an Ancestral Spirit (as per the Tien'Chi national). This Ancestral Spirit is furthermore modified to produce more Ancestral Spirits, which are themselves modified to produce Ancestral Spirit-producing Ancestral Spirits. The province itself contains 4 Graveyard magic sites.

Thirdly, I'd like to see a forest province named 'Bel'Shamharoth', that would consist of an independent Temple, an 'Ancient Temple' magical site, a group of icthytosians-some modified to have Holy/Blood magic, a handful of bloodslaves, and an Ancient Kraken (named Bel'Shamharoth) with 8 levels in Astral magic, equipped with an amulet of the fish and a ring of regeneration, modified to have only 1 eye (not disabled, just modified in this manner from the standard Ancient Kraken).

So you'd have:
64 blood slaves, just milling around
48 regular Icthys,
32 armoured Icthys, as guards
16 Icthy captains (these might be equipped with Stingers to give some magic weapon support, but it's unnecessary)
8 Icthy captains modified to have 2 Holy magic and 1 Blood magic,
and the ancient kraken itself.

A challenge, admittedly, but not something that would require an alliance of several late-game Nations, I wouldn't think. And a fun Terry Pratchet reference.