It's like Godzilla.
Or it's like a big, rampaging mech.
It really doesn't seem that interesting to me, and it would be purposeless, to boot, since only the most ridiculously powerful of characters would be able to even dent it's foot or what-have-you.
Captain, it is not about players being able to tackle it. Very munchkin of you to think about taking it out. If your players try, they will just expend charges or get themselves squashed flat if they are stupid enough to stand in its way. This creature also allows the GM to remind the players of how very insignificant they can be in the scheme of things.
That is why it should not have stats. (Old gamer addage, give something stats only if you want the players to fight it.) It is like fighting the weather or attacking the planet.
This is a force of nature, hurricane, a Godzilla. It is something to drive a number of plots and world events along... Evacuating the city before it gets there, hanging out in a city to prevent looters, scouting out where it might be, the reason why there is a new capital for a really old empire (it crushed the previous one), its presence might catalyze a war, it breaks down a mountain... flooding mud down the lowlands, and any number of things.
This is just a mechanism to foreshadow the power of the ancient peoples, a warning about disturbing things from that time, and a unique bit of chrome for a game world. Go to Comment
Other Kaiju sized golems that were the weapons of that age. This is the last one. The weapons destroyed their civilization (so much so that it does not recognize anyting currently around as a foe). So how much do most being knows about a society of rubble 2000 years ago. We know about Romans/ Greeks but thtat is because our society is built on their foundations. Tell me about the Jawa Dwipa or Aksum or other non-origin cultures. Go to Comment
A non-munchkin way to take out DarkSteel (or at least to prevent it damaging your city) would be to dig a big hole. This could actually be used as an interesting setting for a roleplay adventure. Note, I am basing the following on your statement that:
"I could see a city have a few weeks if not more to prepare for an upcoming visit by DarkSteel" as well as the fact that you can predict the course of DarkSteel to some extent (i.e. it roughly goes in a straight line).
Suppose that in a certain year, a report comes in from the distant edges of the kingdom that DarkSteel has once again been sighted in the neighbouring country and appears to be heading this way. After a week or so it becomes clear that he is heading to the kingdom; furthermore, it appears that there is quite a high chance (30-40%) that he will go through the capital. Let's say this is about two or three weeks before he would reach the capital.
The young king is idealistic, and decides that instead of evacuating he will try and defend his glorious city. Maybe he is partly motivated by the fact that a major city in the kingdom was totally ruined by DarkSteel a couple of centuries ago. He makes plan to dig a huge trench, 50m deep, 70m wide and a mile or two long in front of the capital (Note that it only has to have a vertical side on one side - the other side can slope down (making it easier to dig): DarkSteel would then walk down, not be able to get up the 50m high barrier and then probably turn 90 degrees, walk along the trench and then comes out, but now heading in a direction that won't make him intersect the city.
The king calls in the army (5000-10000 people at least) and presses in to service much of the labour of the city (probably not too hard if he pays them - one sort of labour is as good as any other). Remember, he's idealistic so he's not going to stint at spending money: he pays to get in expert diggers and anything else he needs. He should be able to get a force of 30 000 men or so working on it or more, which would easily be enough to dig the trench (even assuming zero magical aid). It also presumes the city isn't built on hard bed-rock.
Anyway, give your PCs a role in organising this: huge numbers of people, coordinating labour, dealing with the inevitable panicking people (as some will) and dealing with the problems of people abandoning houses (which might cause crime) as you suggested. Go to Comment
Assuming the hole is roughly triangular, each man would need to dig about 350 cubic feet a day, or about 35 cubic feet an hour. 35 cubic feet is just over 1 cubic metre. I'm pretty sure I could dig that out in an hour just with a spade. Remember too, they might have a) more than two weeks (Moonhunter said several), b)more than 30 000 men (Rome had a population in the hundreds of thousands) and c) magical aid. Of course, it will be a mammoth undertaking (and one that may not work), but I think it is definitely possible, just difficult. Go to Comment
It's a non-sleeping version of the terrasque with a bit better flavor. I'm surprised he doesn't have more explanation other than "He was built eons ago and is looking for his last foe". What foe could be so colossal and so powerful that such a monster would need to be constructed? Surely that entity would have left a mark or legend. Go to Comment
Since the Hearthstones have to be enchanted to a spot, you would only be able to find them at waystations and other well travelled camping spots. The flaming discus is out, but the interrogation device could still work, just more vlad the impaler style.
Imagine a holy city with intricatly carved stone courtyards. Invading army comes to strike down the 'heratics'. Army enters courtyard, a single word is spoken, army falls. Cooool. 8)
When I think of the way they are carved, I think of something like a more Elf-centric Aztec calendar, complete with face in the center.
Other than that, Shadow has said everything I could think of (Heating, weapon, communication), so....