You can make one creature/monster from folklore real. Which one?

You are granted the power to create life from nothing, but there are some very specific rules and limitations. You only get one attempt to use this power, and you can only use it to make a type of creature/monster from folklore real. Specifically, this means the following:

• The creature must come from folklore, not mythology. So, deities, demigods, powerful (godlike) supernatural beings — out. Trickster animals, ghosts, fairies, "ordinary" monsters — in.
• Similarly, the creature/monster must have originated from some kind of generalized oral tradition/stories, and not specific fictional works like books, music, plays, TV, movies, etc.
• Extraterrestrial beings, or "aliens," aren't allowed. The creature/monster from folklore must originate on Earth.
• It must be a general category or type of creature/monster, not a specific individual. Vampires and sea serpents are OK, but Dracula and the Loch Ness Monster are not.
• The creature/monster must not have ever existed in reality. So, let's say you decide to create a fire-breathing dragon and amazingly such creatures did in the very distant past exist. Then nothing will happen and you'll have used up you one shot with the power. (But at least you'll know that fire-breathing dragons did at some point — or maybe secretly still do? — exist.)
• Whatever creature/monster you create will be known to the rest of the world upon its creation. So, you don't get your own personal leprechaun. Instead, enough leprechauns would materialize around the world and be seen for people to realize they're real. The world won't be overrun by whatever you create, at least not overnight. A sustainable population is what's being created, but after that whatever happens, happens. We could live in harmony with a population of werewolves or sasquatch, or they could breed or infect enough humans to create havoc, or they could be hunted to extinction.
• Finally, no take backs. Once the creature/monster is in the world, we have to deal with it.

What are you creating, and what do you think/hope the outcome will be?