We've known Greymane was on his way to Heroes of the Storm since BlizzCon, but today he finally entered the nexus—and more importantly, we finally got a look at his abilities. While transformation being a part of his kit was sort of a given, I wasn't sure how they would go about implementing that mechanic. Whether as a Heroic ability like Muradin's Avatar, not directly controllable like League of Legends' Gnar, or just simply pressing a button as part of his passive.
As it turns out, it's pretty close to just pressing a button, but with a little bit of a twist. Greymane is ranged as a human and melee as a worgen, and his transformation is tied to his E ability. As a human, it lets him dive into an enemy and transforms him, but as a worgen it's a defensive tool used to jump away from danger and change him back. Practically, this means Greymane operates as a somewhat standard ranged assassin with the ability to leap in and finish targets off at will.
Greymane is available to purchase in game right now, and you can read the full patch notes here, which doesn't include much beyond his release.