I experience a lot of secondhand embarrassment when I hear someone in the world of video games attempting to rap, but streamer MelloFlowz really pulls out all the stops with a couple bars about, well, streaming and Mega Man.
The link between video games and hip hop is a strong one. Video game soundtracks, especially those that we might think of as "classic," are built out of the same loops and pieces that are easily repurposed to make good ole fashioned beats (a current favourite is the use of a Chrono Trigger sample in a very explicit Fatkidsbrotha track).
MelloFlowz apparently also just breaks out into a freestyle every now and again between speedrun attempts.
And you can check out the beat-making method in a longer stream of beat creation.