This term is used to show that someone has a lot of rizz. It is the combining of the term rizz and the book The Wizard of Oz, it is just a title that someone gives themself or others to say they have rizz, like the title Rizzly Bear.
Dude 1: "Hey bro check out this girl I just bagged"
Dude 2: "Damn bro, you're the Rizzard of Oz"