Where can I learn MyBB Plugin Development?

There's literally one video on YouTube that shows you how to develop MyBB plugins and can i tell you it's down right outdated. I've checked out the Official MyBB Documentation but that's terribly documented and is only helpful when you already know quite a lot about MyBB itself.

I am also interested in this, NulledBB is basically the same type of community I want to create but for a gaming site.