From Dragon Quest Wiki
Quest #112 - "Ranger Changer"
Location Heights of Loneliness - Entrance
Availability Upon arriving at Heights of Loneliness.
Requested by Odval
Fulfilled to Odval
Item Required Kill 3 Hocus chimaera using Poison.
Reward Ranger class become available.
Detail You accepted Odval's challenge at the Heights of Loneliness. She wants you to use Toxic Dagger to envenom three Hocus chimaeras and polish them off with Poison alone.
Hint for solution Have a thief equipped with a knife in order to use the skill. Then equip your party member with Poison needle, this make sure that you can poison the enemy but don't kill them. When you Poison a Hocus chimaera, defend and wait until it finishes its miserable life. Cast Antimagic if you can to prevent it from healing as it is prone to using Midheal.
Repeatable no