User blog comment:Mckrongs/Monster Hunter 4 for the Nintendo 3DS/@comment-6050823-20130924212543/@comment-6050823-20130925225245

Alright here is better explanation of it(Atleast I hope)

Freehunt can only be done offline.

The Custom Quests can only be done online or just by playing in the Guild Lobby offline.

You can't bring any other hunters in freehunt, only in Custom Quests.

Yes, you can hunt them in just about any level but, you need to unlock them first or just kill a Low Rank version of it so, you can hunt it in Low Rank Freehunt or kill the High Rank version so, you can hunt it in High Rank Freehunt.

Kirin, Yian Kut-Ku, Velocidrome, Basarios, Yian Garuga, and their subspecies only appear in this area(Velocidrome and Yian Garuga don't have subspecies).

You unlock the High Rank version of Freehunt by killing Daren Mohran in the Guild Lobby Offline or Online(Thats atleast how it went for me). The High Rank version of monsters appear in the Unknown Sea of Trees Freehunt after killing or capturing them in a High Rank Quest in the Guild Lobby Online or Offline(The same also applies for the Low Rank monsters but, you can have them appear in the Unknown Sea of Trees Freehunt by killing or capturing them in Village Quests or in the Guild Lobby).

After a certain amount of time and enough damage isn't done to a monster, it will escape from the hunters reach and another monster will replace it.

I hope this explains it a bit better.