Lots of Heroes of The Storm news from BlizzCon, but the most interesting by far is the reveal of Cho'Gall.
Heroes of the Storm fans received a fairly healthy helping of information on upcoming content at this year's BlizzCon, with Blizzard revealing a new game mode - Arena, a new battleground - Towers of Doom, and four new heroes - Genn Greymane, Lunara, Tracer and Cho'Gall. Cho'Gall in particular is probably the most interesting reveal, as he is a single hero that is played by two players at the same time, with each player controlling each head.
For a little bit on exactly how Cho'Gall will work: when picked, he is split into two "heroes" - Cho is the Ogre Brute playstyle of the duo, who controls both the movement and auto-attacks of the Hero, while Gall is the caster, constantly using low cooldown + high impact skills, so he can stay active throughout the game. They have some combos that reward co-operation, for example, Gall can cast a Rune Bomb bouncing bomb-type attack which Cho can then detonate with Rune Blast. Check out his Hero Page for more info.
You also don't have to actually own Cho'Gall to play as him. If one player who owns the hero picks him, any other player can choose to play as the other head, regardless of whether they themselves own the hero. Additionally, all BlizzCon attendees and Digital Ticket holders will get the hero for free, and everyone else can earn the hero for free by playing at least two games with another Cho'Gall player.
As for the other heroes: Genn Greymane is the leader of the Worgen, and as such is an assassin champion that can attack both in human and Worgen form, while Lunara is a Dryad ranged hero. As for Tracer, we didn't actually see her in-game, but we know she exists as part of the Overwatch Origins Edition bundle.
Moving on to the new maps: Towers of Doom is a Halloween themed map which has players destroy enemy "Towns", which captures them for your own team.
Lastly, the new Arena mode pits teams of random heroes against each other in an objective-less battleground, similar to League of Legends's popular ARAM (all random, all mid) mode.