The Flash had a great first season, ending with a cliffhanger of a conflict that will easily serve as story for The Flash Season 2. This is what we can tell are the best The Flash Season 2 Spoilers as well as its possible Release Date.
Some die-hard fans of DC Comics may have been upset that when the character of Firestorm was released, he was not shown as having his matter transmuting powers. As it turns out, Screen Rant reveals that there was supposed to be a scene where Firestorm was supposed to turn a thermometer into a daffodil. The scene was edited out, but it could easily become a factor in The Flash Season 2.
As far as what else will happen in Season 2, the Season 1 finale set it up a possible trip to the multiverse. Grant Gustin has told Comicbook.com that "I think we're going to start showing Earth-One and Earth-Two in the near future". For those that are unfamiliar with the DC Universe, there are stories that take place in the multiverse, and the two most famous locations are Earth One and Earth Two. On Earth One is the Silver Age Flash Barry Allen, and Earth Two has the Golden Age Flash named Jay Garrick.
The Flash comic once had a story called "Flash of Two Worlds", and it introduced readers to the concept of the multiverse and allowed DC to bring back its Golden Age versions of their characters like the Jay Garrick Flash. This has led to various crossover stories in the DC Universe, and there was an attempt in an eighties mini-series called Crisis on Infinite Earths to re-create the DC Universe into one timeline.
Of course, the DC universe is ever-changing and constantly being rewritten. However, the idea of Earth One and Earth Two could create an interesting conflict for not only The Flash, but this could spill over on other DC shows like Arrow and a new show coming in 2016 known as DC Legends of Tomorrow.
Other rumors of Season 2 of The Flash Season 2, according to the Latino Post, include and appearance of Wally West. For those unaware of the Flash comic, Iris West once had a nephew named Wally, and Wally got powers and became a speedster known as Kid Flash. Kid Flash eventually became The Flash, but that is another story.
TV Line said that the CW is casting a "spunky, fun, and funny" cop named Wendy who will be Barry Allen's love interest. Viewers should also expect to see the return of Gorilla Grodd, in a bigger role. Also, the Reverse-Flash is also expected to make more than an appearance.
As far as the release date or season premiere of The Flash Season 2 will occur, Den of Geek has some theories based on the Season premieres of seasons of Arrow. Every season of Arrow has premiered the Wednesday night before the start of New York Comic Con. This means that Arrow season 4 will begin on Wednesday, October 7th, (one day before New York Comic Con begins). Since The Flash premiered the night before the Arrow season premier, then The Flash Season 2 will probably begin on Tuesday, October 6th.