"The Flash" season 2 could likely hint the return of Gorilla Grodd and Gorilla City in future episodes, as well as Zoom's identity could possibly be Earth 2 version of Eddie Thawne.
It seems that the new episodes of "The Flash" season 2 next year will be focused on Barry Allen/The Flash and the S.T.A.R. Labs travelling to Earth 2, the home of that universes Jay Garrick (Teddy Sears) and Harrison Wells (Tom Cavanagh). Gustin tweeted an update on his Twitter page stating that they are currently doing episode 14 for season 2 before the Holidays and teased that this episode will "blow everyone's minds", hinting something big will happen soon.
"The Flash" season 2 will introduce two new characters in the show as Scottish musician and filmmaker Adam Stafford is cast as Adam Fells/Geomancer. Geomancer was first spotted in several behind-the-scenes images that were leaked throughout Twitter as the DC character will be fighting Jay Garrick and he is described as a very powerful and dangerous Earth 2 metahuman with ability to make earthquakes and plans on doing a lot of damage in order to draw out The Flash into fighting him.
The second character being teased in the show is Eliza Harmon, another speedster in the DC comics. In the comics, Eliza obtained her super speed from Lex Luthor's experimental program called "Everyman Project" as she was a fan of the Kid Flash. The show's version of Eliza Harmon is depicted as a brilliant, but disturbed scientist with split personality issues being compared to that of Dr. Jekyll and Mister Hyde, and she teased to appear in episode 16 of the show, Moviepilot reported.
Aside from the new characters, Youtube channel Emergency Awesome stated that Gorilla Grodd could return in new episodes in season 2 and this time Gorilla City will be heavily depicted in the show.
According to Emergency Awesome, producer Andrew Kreisberg and the rest of the production could be doing more Gorilla City works in the flash as someone from "The Flash" production has connections for the props used in "Planet of the Apes" film. The production team will likely borrow these props and used a mixture of ape costumes and CGI for the Gorilla City episodes since doing full CGI on the gorillas already cost heavily in the show's budget. Emergency Awesome added that Gorilla City episode could be a two-part special and will likely introduce one of its residence Solovar in the show.
Lastly, a new theory on Zoom's identity has been hinted to be an Earth 2 version of a season 1 character as the evil speedster is theorized to be Earth 2 Eddie Thawne ComicBookResources reported.
Earth 1 Eddie Thawne (Rick Cosnett) killed himself to stop Eobard Thawne/ Reverse-Flash (Matt Letscher) from killing Barry Allen and everyone else during the season 1 finale. Eddie's corpse was absorbed by the singularity possibly transporting him to Earth 2 and probably experimented on by Earth 2 Harrison Wells. Another theory suggest that this could be an Earth 2 version who has somehow affected by the Particle Accelerator and drove him mad for power.
Other possible characters hinted to be Zoom are Earh 2 Barry Allen, Joe West (Jesse L. Matin) and Henry Allen (John Wesley Shipp)
"The Flash" returns on Tuesday Jan. 19, 2016 on the CW Network.