Phantoms were added in 1.13, and I'm not sure what people were thinking when voting for it at Minecon 2017. In my opinion, this is the second most annoying mob in all of minecraft (#1 being baby zombies and husks). It appears when you go three nights without sleeping, but thankfully they are undead so they don't bother you during daytime. These flying terrors drop phantom membranes, which can be used to fix elytras (or you can just get Mending).

https://minecraft.fandom.com/wiki/Phantom

Credits: I got the textures for the Phantom at https://www.tynker.com/, which is a coding website for kids, including Minecraft coding.