Right after the prologue and the intro, a familiar and serious violin melody plays as seconds remain before Gon, Morel and the rest enter the portal and face the Royal Guard. What's the name of the soundtrack?
The title is Mystic Land. It is found in the Hunter × Hunter (2011) Original Soundtrack 1 album as the 27th track. You can listen to it here to verify: https://www.youtube.com/watch?v=EQlALgZ4o5M&index=27&list=PL5pQzc8WlbS__YtYTn12AxaI7wJpRG6WY