Battling a Clockwork Goliath [PF]

[Govinator]

So in my Pathfinder game there is a clockwork city defended by all sorts of varying clockwork constructs. The big bad capstone defender of the city is a gargantuan clockwork goliath that stands over the city gates, acting as a sort of Colossus of Rhodes that can wreck invasions.

My players are working for a rival nation that is heavily influenced by the Roman empire, and they would like very much to conquer this city. However, they are very low level at the moment (just hit level 4) and the CR for fighting a clockwork goliath is 19. Suffice to say, WAY out of their league.

Now if I know my players, they are not likely to want to wait around until they get to the point where they could take on the goliath themselves. So I am trying to think of alternatives that they could take in order to bring down said colossus and allow the Roman-esque forces to take the city.

Info/Ideas I have put into place already:

The city is situated in an area that has violent lightning storms every spring.
To combat this, a massive spire was built that acts as a lightning rod [clockworks are vulnerable to electricity]

I am planning for them to do some sort of sabotage/destruction to destroy the spire, but the storm itself simply won't be enough to take down the colossus. So this is where you come in!

What are some options that they could go about taking in order to do this? I rather like the idea of trying to recruit a similarly sized/powerful ally to fight this colossus but what would feel appropriate? What other measures could they take?

[Deathkeeper]

They could ally with a blue/bronze dragon that could wreck with its breath. Or thunderbirds. Extra points if it's a special, extra-large thunderbird. If so, it must be yellow and recruited with the use of a small spherical artifact. Just kidding but really those are the two lightning creatures that come to mind.

Also, two words: rust monsters. It's absolutely evil to let loose those things on a machine city.

[Doorhandle]

Unlike most golems, it's not immune to magic. Enough magic missiles will take it down. GETTING enough is your own problem.

Constructs in general seem to be really simply programmed, so you could potentially lead it over a huge drop. This is complicated by the on-board cannon it has, however.

Golembane scarabs, as well as construct-bane weapons in general will help. construct-bane ammo is basically ideal.

Electricity damage will help, but any energy damage is good: it has no resistances. Note that reflex is it's best save however.

If you DO get another big bruiser to fight it, have the players ride on it and help: it'll make them feel more engaged, and it will be a cooler fight.

Lightning elementals gain an attack/CMB bonus against metal creatures, and do electricity damage (nach). An elder lighting elemental, despite it's lower C.R, could change the tide, particularly if it trips the bastard. It's basically ideal.

Calikangs are also ideal due to their electricity breath weapon: keep hitting it with weak electricity spells in order to A: heal it constantly and B: allow it to reuse it's breath weapon.

You could have them bring a siege weapon to do it in: they'll probably need extra crew for anything larger than the basic 6d6 cannon, though. scrolls of magic siege weapon, or energy siege shot: electcity would be helpful as well.
Plus, they'll want to be at the maximum range possible for using one, to prevent return fire and to delay melee assault.
You'll want to avoid the firedrake if possible: sure, the goliath has no special resistance to fire, but reflex is it's best save.
Also, they'll probably want to keep it: maybe have it on loan?

A cool Idea would be to have them ride around in a steam giant (http://www.d20pfsrd.com/equipment---final/vehicles#TOC-Steam-Giant) while battling the giant.
An airship would also be appropriate.

[mregecko]

This thing has a - INT and no ranks in any skills (like Perception, for instance).

Buy a casting of Greater Invisibility and plink it to death from range with Magic Missiles or Snowballs (the spell, not the object).

It also has no magical attacks. Are there any low-level incorporeal undead that can damage it? A casting of Command Undead would get you a fighter that can't be hurt by the Goliath.

[Govinator]

The idea of having the players ride on the big bruiser (if they find one) is awesome, that's a great idea!

Also, @mregecko, incorporeal undead could certainly be an option as well, but this city also has a fair number of casters. They could just cast magic weapon on a few of the normal clockwork soldiers and tell the soldiers to chop at the incorporeal undead. I think the players would have to find a large number of such undead in order to do any significant damage because of this.

Rust monsters... now that is just plain evil, glorious and evil. They could try to arrange to let some loose in that city! But how could they do that? Find a wooden cage to stuff them in, or something? Can rust monsters be summoned?

Also, please, more ideas! These are really great, I appreciate them so much!

[Kazuel]

What about getting it to follow them through the city and let it destroy the city. Once it becomes apparent that its doing so much damage, other city defenders would have to bring it down.

[Deathkeeper]

The idea of having the players ride on the big bruiser (if they find one) is awesome, that's a great idea!

Also, @mregecko, incorporeal undead could certainly be an option as well, but this city also has a fair number of casters. They could just cast magic weapon on a few of the normal clockwork soldiers and tell the soldiers to chop at the incorporeal undead. I think the players would have to find a large number of such undead in order to do any significant damage because of this.

Rust monsters... now that is just plain evil, glorious and evil. They could try to arrange to let some loose in that city! But how could they do that? Find a wooden cage to stuff them in, or something? Can rust monsters be summoned?

Also, please, more ideas! These are really great, I appreciate them so much!

Rust monsters are usually contained with wood, Iron-wood, and I suppose magic-enhanced glass or bone is also viable. I remember fluff somewhere in PF that said some cultures use them occasionally as living weapons if they don't have much metal to lose, so the party might have to go underground for a spell to track down one of those tribes.