What mythical creature should exist and why?
I think vampires but, only if another equal opponent exists to balance the food chain.
There are several things that one can do that a regular lifespan would never allow them to do. Being injured so easily prevents one from doing many things as well.
If you ever got bored of your life, if you don't get killed first, there are methods to end your life. Go pick a fight with the government or something.
Most logically thinking I think centaurs should exist.
I mean they don't have any crazy power that would be unreal.
They are just mutated horse and human.
Mostly known with a bow or a spear
I think Phoenixes should exist. The reason being that they would be extremely rare and uncatchable. They would appear in the sky as people watch in awe driving their brains to believe that there is much more mystery and beauty in this world. Unimaginable things, unseen and untouched that must be discovered and preserved., It would be a sign of hope. Maybe finding a phoenix feather or down could provide a cure for any types of diseases BUT if people try to monetize it it would vanish. It could be burned and released into the air and as the particles expanded throughout the atmosphere anyone who breathes it in will be cured.