[HoneyBadger]

I always wanted the Ageless Olm to be more interesting, too.

It seems to me that it ought to fulfill some kind of mental "mobile artillery platform", a sortof intellectual's SC, to give you a ranged combat boost. Something with the ability to deal out serious stopping power, so that, atleast if you connect it to your starting army, it should function as a powerful thug, and give you some dividends, in return for protecting it on the battlefield.

And it's got the rare and precious "mud bless" down pat. Earth plus Water should equal Gold, for a ton of Nations. Sadly, the Oldest Olm never seems to get matched up with Nations that can really harness the gifts it brings.

Another possibility would be to hand it over to some underwater Nations. Let it give Nations like EA Aboleths a leg up on making landfall... Again, nothing materializes, even when clearly, it makes sense for there to be a synergy between mud dwellers, and the Mudhole God.

If it were me, I'd certainly give the Olm some major Stealth (if anyone knows how to hide, it's a critter that's spent almost a thousand years in a cave), increased Defense (13+) and maybe 50% fire resistance (slippery when wet!) with maybe the ability to fire multiple Mind Blasts at a time. A bare minimum of 3 seems reasonable for such an "artillery SC". That would make it reasonably tough, on land or in water--and be enough to give EA Agartha a decent chance, in the ocean.
And since it's a size 6 beasty, maybe the ability to trample? Lacking real melee ability, trample would atleast give it a strong defensive weapon, and allow you to occasionally take advantage of an enemy's weak position, with a stealthy stampeder. This would negate the Life Drain in a lot of situations, but that would serve as a balance against giving the Olm a more unique character, and one perhaps more interesting than slow shielded squishy death.