nerd griping, feel free to ignore
So, I made the mistake of watching the trailer for the new Ghostbusters film. Stranger Things with Night in the Woods. The Monster In The Mine Is The Ghost Of American Decline stuff. Fine, whatever; I won't watch it anyway. What really stuck out to me—because I’m an insufferable nerd—was the little Stay-Puft Marshmallow Men. There are a load of these tiny "cute" lads running around on a shelf like tiny Minions, freaking out the squares, presumably demonstrating that there's something spooky going on.
For context: in the original Ghostbusters, there's a point at the climax of the film where the villain, Gozer the Gozerian, calls on the protagonists to "choose the form of The Destructor"—the shape that it will take in its destruction of the world—and one of the heroes imagines "something that could never possibly destroy us": the mascot of the (fictional, in-universe) marshmallow company. You've seen Ghostbusters; you know this. The point is: the association of the marshmallow man with supernatural phenomenon was a highly specific and contingent thing. He's not a magic marshmallow man, he was just an image that was used in one context, but now he's part of the visual lexicon of Ghostbusters, along with Slimer, the logo, the suits, the car, etc.
While I'm sure there will be a reason for the tiny marshmallow men, this is an example of a phenomenon that a lot of things suffer from—but particularly “nerd media” properties. Things that are particularly iconic or resonant or visually distinctive in the breakout initial film or series or what-have-you are brought back in later instalments to reassure the viewer they're watching One Of Those, regardless of whether it really makes any sense for them to be there.
The example I think of most often is that in The Empire Strikes Back, Han Solo is frozen in carbonite as a test run to see whether it would kill Luke Skywalker, the person they really want to capture and freeze. Note: a test! Because it had not been done before! Yet, in almost any Star Wars extended universe media you care to name, folk are getting carbonite'd all over the place like it’s SOP. The Old Republic MMO is a particularly egregious example of this, given that it's meant to be set centuries before the events of Empire.
This seems like the sort of thing there should be a name for—on TV Tropes, maybe—but I’ve looked for it using the most prominent examples I can think of and found nothing. The best description I can come up with is some sort of 'iconographic flanderisation'. Hopefully someone else can come up with something a bit catchier!