Monkey_T in Dark Cave holds the key to the level 30 and under boss quest. In order to complete the quest you have to bring Monkey_T 3 addax horn and then he will teleport you to the boss level where you can try to get Master Mon's fur. (Just kill addax there in the dungeon to get the horns).
Be forewarned, this is NOT a quest to take when you are level 20 and just getting started. This is NOT a quest to try alone. Get a party of seasoned level 28-30 adventurers and go for it. If you try it by yourself, even with good equips you will find yourself hard pressed and failing.
If you fail the quest you will have to present 3 more addax horns in order to try again.