No more issues with the sound or the framerate. Yaaay~
Dark Nep Hilim Lel is one of the few bosses which don't require you to attack, attack and attack. In this fight you actually have to run away and dodge the boss' attacks until you can trap him. Although this makes the game a little bit more than this:
http://gtm.steamproxy.vip/sharedfiles/filedetails/?id=252490930 this fight is still very easy.