Othernesses are more like the Colour out of Space than shuggoths.
Shuggoths were basically as described-big blobs of extremely muscular bubbles-strong enough infact to be used consistently as living engines for millenia-so like a pet dog powerful enough to run an automotives factory for a million years by running on a treadmill. They also had the ability to mutate at will-growing eyes, hands, mouths, whatever, but were initially created with no free will-mindless, formless slaves. They only developed free will gradually through chaotic evolution.
So maybe they could be another kind of shapeshifter that eventually turns into a form that can go rogue like the Eater of the Dead.
Before my computer died I was working on a summons for my Fthaggua nation that was meant to invoke C'thulhu, and compete with Tartarians. They'd be size 6 giants with 3 lifedraining tentacle attacks, most slots, and an insanity gaze-a bit like the Void Lord, but with only 1 astral, so you'd have to empower them a lot, or they'd be very vulnerable.
The Wendigo would make a good endgame SC-in Inuit myth, the Wendigo is this gigantic bloody red skeleton that hunts the arctic and freezes people solid that it comes across, and is basically the essense of fear-so maybe a critter with natural soul-vortex, high chill aura, and high fear? It's always struck me as very Lovecraftian, so it would be perfect for late-age Atlanteans.
The Lesser Key of Solomon
(a really good article can be found on Wikipedia)
http://en.wikipedia.org/wiki/The_Lesser_Key_of_Solomon
is filled with really bizarre demon princes and kings-nothing like the standard "Balrog" types.
I love the idea of the dragon egg above, hatching and then growing over time. The way I'd do it would be to make the egg itself a sort of "doomsday weapon. It would be very tough but immobile, with a good strong fear aura, so that it would be pretty invulnerable and would benefit a defending army built around it. The dragon, once hatched, would be a rogue-again like the second form of the Eater of the Dead-so that you wouldn't necessarily want that egg to get hatched. The dragon would quickly become very powerful, instill enormous unrest, and in general be the world's biggest headache for all concerned, just like dragons in real world myths are supposed to be-forcing your enemies to consider the consequences of *winning* a particular battle, sort of the Dominions version of the A-bomb.
I'd still like to see a Niefel Jarl on a wooley rhinocerous-that's gotta be pretty hardcore SC.
Speaking of Niefels-how about giving them Surtr as a unique summon? Make him the fire version of a Niefel Jarl and arm him with a Jotun-sized fire brand.
Later versions of Jotunheim could get the giant Bolverk-blind in both eyes, with a limp, and quite old, but very impressive Forging bonus and otherwise decent stats. Comes with a hammer that curses whatever it hits.
Hel would make a good unique summon for Helheim-giant sized immortal necromancer/valkyrie with natural Awe and Fear, half beautiful goddess, half undead hag.
The egyptians had this god of the underworld that was this gigantic snake which had growing out of it's shoulders (snakes have shoulders? *shrug*) two *other* mummified humanoid gods, from the torso up. Seems perfect for a C'tis unique summon.
Also, just because something isn't humanoid doesn't mean it can't have slots-animals in particular can wear barding, for instance. And monsters can be ridden as mounts, also. Look at Dune-if you can ride a 400 meter long sandworm, what *can't* you ride?
By the way, H.P. Lovecraft wasn't the only writer who came up with a unique environment of monsterous/godly creations. Jack Vance's Dying Earth, William Hope Hodgeson's Night Lands, Michael Moorcock's Eternal Warrior, Fritz Leiber's Lankhmar, even Clive Barker's Imajica and Terry Pratchet's Discworld are all excellent sources for artificial mythology. Lovecraft, himself, credited being influenced by Lord Dunsany, M.R. James, Arthur Machen, and Algernon Blackwood. And just about every author of the period: Lovecraft, Tolkien, Robert E Howard, etc. etc. etc. was influenced by H. Ryder Haggard.
And one that wasn't, particularly, Mervyn Peake, who it seems to me drew more on Lewis Carroll-another fine source of myth, is one of the best.
So there's a lot of stuff out there to draw from, that can get us past the idea of "more of the same, only bigger"
And with Construction, we have the ability to create summonable units that fight smarter, instead of just harder. Easily summonable engines of war, as well as field defender units, become possibilities. Imagine a unique massive, mindless, mechanical spider-mech, ala Wild Wild West, which produces-instead of being destroyed by-flying mechanical hornets that move extremely fast and deal out death poison that can drop an elephant? Or a unique Watcher-themed unit that is GoR? Or a unique Electric Monk (ala Douglas Adams' Dirk Gently's Holistic Detective Agency) that automatically casts Banishment, and doubles itself every combat round. Or submersibles that produce tough high seige bonus, high patrol bonus defenders, to take the place of PD when you're under water. Steamcannons could have unheard-of seige capabilities, move easily through any given terrain, and transform into artillery in combat, ala Starcraft. Maybe instead of larger mechanical men, they're size 1 instead, but have 4 attacks per round? Or a size 6 unit that does nothing but churn out a constant stream of longdead that have armour and weapons bolted directly to their bones? Or an "iron cobra" unit with high stealth and patrol bonus that can't fly but can reach any land province in a single turn, because of it's extremely high movement-rationaled in-game as "dimension-shifting".
No unstoppable juggernauts, no real SCs infact, but good solid units that fulfill a late-game need.