From http://heavy.com/news/release-the-kraken-meaning-sidney-powell/ :
According to Live Science, it comes from the movie “Clash of the Titans,” in which Zeus, king of the gods, gives the order, “Release the Kraken!”
“The term is becoming a cult-like catchphrase,” the site explained.
The Kraken is “a massive multi-limbed monster that roars menacingly and can destroy cities with a sweep of its arms.” Thus, according to Live Science, it is the “ultimate threat” and “Zeus’s nuclear option to teach unruly and disrespectful humans a lesson they would never forget.”
Ooooh...