Judging from the clothes, that looks like a Warlock. And being a Warlock, it could be the Sunsinger focus special, which if I remember correctly massively decreases the cooldown times of your abilities among other things...and one upgrade lets you revive yourself with it's activation. Given how the gif starts, I think he probably Blinked into combat and immediately activated it, ready to initiate carnage (since the Titan crouched to the side, unable to hit the Acolyte right in front of him with his shotgun, doesn't seem to be bringing it to them...for shame, mister Titan! Just punch his lights out!). Edit: and it's only after the fact that I realize you're not asking "what's going on here?" but "how does it feel?" which leads me to believe you probably already knew everything I just said...*shrugs*