Actually I never felt like I had any reliable counter for Caelum's Elemental Queens - they pretty much owned my pinocchios when they first met, and I went totally paranoid with avoiding any further confrontations, especially when I found out that they can be resummoned after death. Lorak leaving gave me somewhat free reign in the area, as Bluerobin did not use them as aggressively as his predecessor did - which is understandable caution on his side, but still.
I've been summoning Tartarians for a while now, and had one titan commander with a bunch of other Tartarians and a Gate Stone jumping around the map with impunity and giving off a kind of game-breaking vibe. Same with that teleporting Pinocchio(with boots of the planes or somesuch trinket). Perhaps there is some reliable way of countering an army and a SC that can leave the conquered province in a magic phase, but I don't know about it.
One other army was made up of a pinocchio with a flying ship and some dozen or more mammoths stolen from Caelum. As great as the idea of pachyderm paratroopers sounded, I never used them in (serious)battle.
Pythians indeed couldn't stand their ground against Zantaron and his army of dustwalkers, but it was one of those late-game armies enchanted with everything one can possibly want to cast, and carrying half of the world's artifacts, that can get pretty much unstoppable. On the other hand, should Master Enslave work(you'd need some serious penetration boost for dustwalkers' high MR), that could turn the tables - it took me years to build that army.
I was just about ready to solve the R'yleh Problem, after a year of feebleminding Ignus' mages with Strands of Arcane Power, and finally being able to cast Master Enslave, which probably could finally net me some decisive victory. The amount of resources that I've sunk in that damn lake was unfathomable.
I've seen that Marignon was moping up the remanants of Ashdod, and sported quite a well-developed armies, so maybe he'd take over the anti-Agarthean duties from R'yleh later on.