The Glow Squid was added in last week's Minecraft snapshot 20w03a, but it doesn't actually give off light. So, I had the idea to write a datapack for it. It uses the new Glow Lichen to temporarily place what are essentially invisible light sources in the glow squid as it swims around.
Some footage of what it looks like:
I also made a short devlog-ish video that gives some detail about how the datapack works, and some interesting results: