Just like last time, these aren't mine, just topics others posted on /r/worldbuilding that I found interesting but were removed by the mods.

I should really just start copy-pasting them here because I've started to get a sense for which topics are likely to be removed despite generating a lot of fruitful discussion.

The coolest idea I read over the last few days was the idea of "living" fire. Not at all uncommon in fantasy but the way the OP described it made it stand out to me. It's not sapient or even clever, rather it's more like a fungus. It can seek out fuel and avoid water. You can "train" it to prefer (or dislike?) certain types of wood. The longer it burns, the more water it takes to extinguish and the less wood it takes to keep it going.

You can "breed" a new fire from an old one by lighting a new fire with an ember from the old. The new fire will inherit some or all of the traits of the old, the hardiness and wood preferences etc.

The first thing I thought of was a pyromaniac breeding fires as attack animals.

FFFIRE! yeah, eheheheheehe! ffffffire! heheheheheehehe!

Another casualty of the mods was someone asking about a language for sapient hyenas, with the understanding that a hyena vocal tract can't produce the same sounds as a human. I just pointed them to my wiki article on Commonthroat hoping it would give them ideas. I love xenolangs and always enjoy seeing others' try to tackle them.