The video appeared online shortly after several other leaks about Deadlock, Valve's multiplayer team-based action game.
According to insider Tom Henderson, the gameplay in the game resembles MOBAs and, more specifically, Dota 2. For example, players need to kill creeps to get currency.
Henderson himself did not publish Deadlock gameplay, but someone did it for him. In the video you can see some animations and some of the characters of the game.
Deadlock has not been officially announced yet, and it's not clear when the action may be released.