As season 3 of The Flash progressed, there were multiple references to Clifford DeVoe (Neil Sandilands), setting him up as the big bad for season 4. According to executive producer Todd Helbing, the Flash season 4 finale is going to set up the big bad for season 5, and most comic fans will be able to figure it out from the threat introduced in the finale.
Helbing told EW.com that the final confrontation between Team Flash and the Thinker is not going to go as most people are expecting:
It's an Inception-inspired episode. Most people that are familiar with comics will probably be able to deduce who the big bad is for next season.
Along with the new threat being introduced we are promised that we'll find out the identity of the Mystery Girl (Jessica Parker Kennedy), who we recently learned is a speedster. It's been speculated that the mystery girl is either Dawn Allen, the daughter of Barry Allen (Grant Gustin) and Iris West (Candice Patton), or Jenny Ognats, their granddaughter — both of whom are speedsters in the comics. But doubt has creeped in over the last few appearances as her reaction to some characters have been less than jovial as her first appearances were.
Who will be the next big bad? Will it be another speedster? And will we ever get Rogue War?
The Flash airs Tuesdays at 9 p.m. ET on The CW with the finale scheduled for May 22nd.