If this had been announced just a few days earlier, I'd have assumed it was an April Fools gag, but Blizzard are (mostly) deadly serious here: Diablo's crumbly old sage Deckard Cain is the latest addition to their fast and accessible MOBA Heroes of The Storm, and he's quite unlike any other character in the game, or many other MOBAs for that matter.
In most other games in the genre, a character like Deckard Cain - an almost entirely non-combat, pure support character - just wouldn't be viable. He can't jungle, he can't grind, he can't zip in for a quick spike of damage to finish off an enemy, so he can't level up by himself. What he can do is support and buff and heal and slow the enemy team down, and thanks to Heroes of The Storm having your entire team share level progression, that's just fine and dandy for the wizened old lorekeeper.
While he has the ability to bash people with his staff for a little bit of damage (and what looks like a fair bit of knockback in the video above), his primary role is keeping his team in the fight. The more teammates he's near, the more resistant to damage he becomes and the faster his abilities recharge. In the middle of a full pack, he becomes frustratingly hard to put down, making him a less appetizing target than most. While hanging out with his friends, his primary abilities involve throwing healing potions onto the battlefield that injured teammates can pick up at will, and throwing out the Horadric Cube in order to slow and debuff enemies.
Making him a far less combative character than most has given Blizzard the opportunity to be a little bit tongue-in-cheek with his skills. His primary Ultimate skill is (as you would expect) Stay A While And Listen, a big conal 'attack' where he pulls out a book and recites such a thrilling tale to the enemy team that any foe within earshot is put to sleep. Even his more aggressive alternate Ultimate, Lorenado, deals little to no damage, instead focusing on knocking the enemy team back and interrupting skills.
The only thing missing from his repertoire is his legendary rapping skills, although I'm sure that's just an oversight and will be patched in soon. Deckard Cain will officially be arriving in Heroes of The Storm sometime this month, after he gets the worst of his arthritic kinks out on the public test server. The game itself remains free to play.