Did you know that informal speech can actually be mixed together with formal speech, in the same sentence? This only happens in some specific situations, but these situations aren't as rare as you might think.
For example, this could be something like mixing the word 나 together with the 니다 ending, or the 요 form with the 니다 ending.
This series has a total of 24 episodes, and if you're a channel member you can watch all of them right now. Each episode will also be uploaded publicly (for free) once every week until it's completed.