9. Deathclaws (Fallout Series)
Just look at that picture. That Deathclaw is challenging you to fight him - he wants a piece of you because he suspects he can take you, and honestly he most likely can. Unless you find an alien gun that kills anything in one shot, these things are quite the challenge, and there are a few reasons why they are tougher than the dragons of Skyrim. Chiefly, they are relentless: it's possible to run away from a dragon, but you just try running away from a Deathclaw. They chase. They chase and they won't stop until they get you. On top of that, these monsters travel in packs, so maybe you do defeat one - you'll do it quite easily, and you'll wonder why I ever bothered including them here. But then, in the distance, you notice that one about twice the size of the one you just killed is running full speed for you, and that the one you killed was merely a baby Deathclaw. Good luck with its angry mom. There's a reason they have the word "death" in their name.