Which fictional creature or monster would you least like to have become a reality?

I luv horror movies! I’ve seen all manner of creepy and dangerous things that are otherwise difficult to define. They usually try to slap a label on it, and then commence to researching how to defeat it or escape it if it can’t be defeated.
There are some so dangerous that every attempt to study them has resulted in disaster, on the screen of course. So which of our collective imaginations’ freakiest freaks would you least like to see become a reality?
There are a lot of options and i find it difficult to choose, but it would have to be something that either crazy outnumbers people and/or control us, like the extraterrestrial slugs from “Night of the Creeps”.

https://youtu.be/_PmPuYg6nqM?is=NGlla7Lywii-ebZk

Or the whatever the heck it was that turned people rabid in “28 Days Later”.

https://youtu.be/mWEhfF27O0c?is=qAsN9-zvQQtFHkvV
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Honestly, something so mysterious and powerful that it could wipe out most of mankind before we could find a solution would be bad too. Like the dragons from “Reign of Fire”.

https://youtu.be/aUXQ2f3GAXA?is=qyLmfFl7PX88-EYT
Which fictional creature or monster would you least like to have become a reality?
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