Thanks to M16 for making a tutorial of this: https://youtu.be/AI6jDVbLLVk

I made my own texture of it cause there's no official texture of it. Anyway here's the facts

The glare is a mob that let's you know when you're in an area for monsters to spawn. The glare flies to dark areas for you when it gets grumpy, you'll know that its dark enough for monsters to spawn.

Some facts here: https://www.youtube.com/watch?v=uYIQsr9vsws