I won't copy/paste his response or anything like that, but I already got a reply from Zillix and he told me I could make gameplay videos using Endeavor. I'll be making video guides and a review of Endeavor soon, and I'll also be checking out his other games. He told me that the music was made by someone else, Hermtheworm, and that he's selling the soundtrack of Endeavor for $5 right now. I may buy that for my own listening pleasure, but for now I intend to just stick to gameplay-related videos.
Also, he gave me the link to a newer website with more updated games, including one he recommended called Terminus, which he says is similar to Endeavor, as it has multiple endings. I haven't played it yet, but I have looked at it and Terminus seems similar in art style. Here's the site:
And I found, from his old site (http://zillix.webs.com/) that he uses a certain program to make his games. Flixel is its name, and if I like it I may actually make Newgrounds games myself. I'll give you any updates on all of what I discussed later.