I have reached Mastery 6 Yi while practicing jungle, and...
Over the course of 30 Master Yi games practicing jungle I have reached Mastery 6 with him, and through that I have learned one thing if nothing else; My team's sole purpose is as a meat shield to soak up CC before I engage, and a distraction so I can push towers elsewhere.
If I didn't have around a thousand support games under my belt, this experience may have made me a very greedy teammate XD