'Lo and welcome to tasvideos, enjoy your stay. To answer your questions:
1.) It depends. You can do a testrun of one level to see how the game works and see how you can optimize this one level, or you can do a testrun of the whole game.
2.A run usually contains only input, so if you do something to mess up the random rumber
god generator, it might desync. Unless you mean RAM Watch, where the RNG change should be displayed.
3.It has something to do with hitting the boss at the exact same frame it hits you. Try to replicate the setup as closely as possible (the bat charging you, you standing on the stairs like this). It isn't that difficult to do.
4.
Here is a good bit of info, you should also check out the authors' comments for the published Castlevania runs. Aside from that, search for something like "Castlevania Tricks" or "Castlevania TAS" on places like youtube, gamefaqs or so. We also have a topic on the game in the forums.
5.I'm sure there are, though I'm not one of them. Sorry, bro
