This includes fantasy and sci-fi.
My choice is the Combine.
A multi-universal species from half-life so absolutely immense and powerful that they reverse-engineered earth's technology, upgraded far beyond human ability, brainwashed some humans and had them invade themselves. They did this and stomped all resistance within 7 hours. This was done by a backwater lesser combine city mind you.
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Post - DBZ Saiyans. This is half-breeds and all Saiyans who fall under the dragonball timeline during the era of the 'Time Police', in which going to Super Saiyan is a common rather than a rarity.