I use GameDVR (agario can take the framerate hit). GameDVR has a bug where Windows won't draw menus until I unplug and replug the monitor after using it (sometimes), so I did try Nvidia's thing. That recorded the start page for agario and my mouse. It was super interesting to watch, but not what I wanted. Maybe it works better for "real" games.
Anyway, everything is shit ;)