User blog comment:Xandermcc/Arrow and the Flash copying each other? (part two)/@comment-31910502-20170503204642/@comment-27700324-20170503205707

Presumably Killer Frost or the villain that Abra Kadabra mentioned who is called Devoe AKA the Mad Thinker. Either way Season 3 mentioned/featured the villian. Just like how Arrow mentioned Damian Dhark.