You can probably guess I have ridiculously mixed feelings about the junk golem.
It’s no secret I don’t like exotic golems. When it comes to golem building materials, if you can't mine it or fire it in a kiln, I am skeptical. And I especially don't like golems with swarm powers (mask golems, anyone?). That seems to me to be antithetical to the core of what a golem is: a big, blocky thing inexplicably brought to life by powerful magic and an elemental spark.
That said…well as someone whose living space is constantly overwhelmed by kipple, I can't help but find the golem’s Discorporate (Ex) ability to be totally thematically appropriate. And as someone who was in elementary school in 1986, the notion of fighting giants made out of junk has an appeal too primal to be denied.
And the golem’s tetanus-causing slam attack? Is that stupid or totally awesome? I can't even tell anymore!
In the end, utility wins out—a CR 4 golem is a pretty useful low- to mid-level obstacle. And junkyards and refuse heaps are exactly the sort of places that adventurers should be spending their time in, especially in urban campaigns. As with many constructs, the most interesting about a junk golem is its creator. Junk is, by definition, what people throw away. The kind of person who turns refuse into a guardian is a person worth encountering.
A syrinx takes control of the city library and archives, and begins consigning “dangerous and seditious” works and memorabilia to a remote annex. Over time the aggregate weight of neglected and suppressed literature forms a kind of miasma. When a malfunctioning artifact is added to the collection, the animating spirit inside manages to incorporate the room’s resentful contents into a junk golem body. The golem has no true intelligence, though, and simply attacks anything that enters its domain.
Junk golems have been rampaging through the city. Ratfolk, the junkyard’s main inhabitants, are bearing the brunt of the populace’s frustration, and cries of “Exterminate the vermin” are common. The actual culprit is a junkyard-dwelling svirfneblin so spiteful his own kin drove him to the surface. Meanwhile, other bad actors are taking advantage of the chaos. In particular, a party of “golem exterminators” are running around town with leashed rust monsters. Ostensibly they are hunting the rogue constructs, but in actuality they are rusting away the locks, hasps, and hinges of shops they intend to burgle.
Adventurers are hired to clean out a deceased wizard’s tower. In addition to identifying (and ideally disarming or disposing of) any traps or hazards, they are supposed to retrieve an odd assortment of items, including a peculiar bronze helm. This is actually a trap on the part of their patron, the wizard’s nephew. He knows that the items are the core pieces of a discorporated junk golem programmed to dismember looters if the helm is disturbed. He knows the key phrase to shut down the golem, but he prefers to watch the party be demolished rather than pay their fee.
—Pathfinder Bestiary 4 132
And then there’s the golem made out of ancient Chinese boat parts. You know, because it’s a junk golem? Eh? Eh? …I’m gonna go now. Have a good weekend.