Fantasy Wildlife
Random thought from early 2025 that I never got around to posting: way too many D&D games and settings treat the stuff the party encounters as familiar. And while that makes sense for some campaigns and settings, with as frequently as games take place in frontier spaces, there should probably be more unknown or unfamiliar stuff. Let players encounter unknown animals and monsters. Consider how many weird creatures from myth and folklore are just distorted descriptions of actual animals, after descriptions of them traveled hundreds or thousands of miles to people who weren’t familiar with the animal.
Tying into this, wildlife in a setting shouldn't be the standard Earth animals (even if they're similar and use the same statblocks). Change them cosmetically to fit your setting. Change them non-cosmetically to fit your setting. As an example, the prehistoric dire wolf was similar to modern wolves but isn't actually a wolf, instead being a distantly related canine. However, it developed similar traits to wolves because it lived a similar lifestyle. Maybe the wolves in your setting aren't canines at all, maybe they're some form of pack-hunting feline.
Just fun things I like to think about.