I was mind-blown to learn that the Game of Life can have a pattern that plays the Game of Life.

The idea that Game of Life can play itself is not new. It has existed at least since 1996 (also here). By 2006, a grid like the one above existed. I learned about Game of Life around 2008-2009. By then, engineers played with the idea of Game of Life which played itself for over a decade. By 2018, a self-replicating metacell existed so a grid like the above would grow indefinitely.

I re-read the Wikipedia article about Game of Life every 3-4 years, it keeps getting better and better.