The Exquisite Corpse.
For those of you who are unfamiliar, the exquisite corpse is a parlor game invented by surrealist André Breton. He and his wacky surrealist friends would get together and make a piece of art using collage. Each person worked on the piece one at a time until it was finished. But there was a trick: each artist would cover all but a portion of their section before passing it to the next contributor. Even artists get stuck, and this was a great way to stretch the creative muscles while also creating a process document.
This translates very well to writing and I often use it as my own game of writing solitaire. If I find myself stuck, I’ll copy a line or two of text from the end of a paragraph into a new Scrivener document and just start writing from there. It doesn’t have to fit with the rest of the chapter, sometimes it’s just a footnote, but it keeps me moving along.