Adding A GUI Image Behind a Vanilla GUI

I'm making a mod based around the old "Thing" Creepypasta (https://minecraftcreepypasta.fandom.com/wiki/That_Thing)

As seen in one of the images, one of its abilities is to appear in the backgrounds of some GUI. I was wondering if it would be possible to have it randomly appear behind vanilla GUI such as inventory or crafting table? I have never used GUI in MCreator before, so even if this was possible, I'm not sure where to start.

(Apologies for the awfully written wiki page lol)