I could do a written guide, or I can do a video guide. I am leaning towards the idea of video guide since it is easier to describe what I want to explain with visuals. What do you guys think?

In addition, should I make an introduction guide that explains game mechanic as well as enemy/boss behaviors?

I thought so. I should start planning out what I want to cover and divide which sections I want to make it as separate video. Any other suggestions?

Sounds like a good advice. Thanks for the input!