Somebody asked me to correct this sentence: わたしはゲームをしながら、おんがくをきくこととユーチューブのビデオをみます。
There are a few things you have to consider here.
First point is, if you are using the "A ながら（、）B” pattern, more of your attention is on the action B. It is hard to imagine you can play a game while paying more attention to listening to music, so the first 2 parts need to be swapped.
Secondly, if you are listing up 2 activities you do, …たり、～たり is better suited than …ことや～. Then the possible correction would be: わたしはおんがくを聞きながら、ゲームをしたり、ユーチューブのビデオを見たりします。
However, if you leave “、” after ながら, that means both actions of “playing a game” and “watching Youtube video” happen while you are listening to music. As it is hard to imagine that you can watch Youtube videos while listening to music, “、” after ながら has to be deleted.
Then the completed sentence is: わたしはおんがくを聞きながらゲームをしたり、ユーチューブのビデオを見たりします。(I sometimes play games while listening to music and at other times I watch Youtube videos.)
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