Guild Wars 2

It’s like a recurring explosion of blackness, and if you angle the camera in the right way you can see other textures appearing, like grass and stars.

There’s one of these in Queensdale, just south of the Scaver Plateau, in the little swampy river a bit east of the skale nesting site. It’s weird. Making noises like something going in and out of stealth, the black wispy stuff. Creepy. Like your screenie, IIRC I believe it’s also happening “on” a plant/bush.