In a surprise announcement, two new Heroes were just announced at The International for Dota 2. The first Hero teased was Mars, which just had a quick still shot and a winter release date. And then, seemingly out of nowhere, they announced that another Hero, Grimstroke, is available to play now!
Dota 2 is free-to-play and all Heroes are always free for everyone. I tested out Grimstroke quickly and have a video of all his abilities for those interested. He’s listed as a support/disabler in-game and his abilities make that very clear.
Source: Destructoid New Dota 2 Hero available now, another coming this winter