David Dastmalchian (Abra Kadabra) previously played a henchman of the Joker twice, first in The Dark Knight (2008) as Thomas Schiff, then in season 3 of Gotham, he played Dwight the leader of a cult inspired by Cameron Monahan's TV version of The Joker, Jerome Valeska.
This is the 64th episode of The Flash and the villain, Abra Kadabra, comes from the 64th century.
Abra Kadabra mentions the name DeVoe when naming arch enemies of the Flash. In the comics, Clifford DeVoe is the real name of Flash villain The Thinker
Abra Kadabra was also an enemy of the Teen Titans.
When Abra Kadabra removes a piece of tech from the time vault, he says aloud, "Thank you, Dr. Wells." Kadabra, being from the 64th century, is probably aware that the item belongs to Eobard Thawne posing as Harrison Wells.