Collect all experience in Shadowthorn Thicket
Experience (level): 20/20
Experience (enemies): 15/15
Secrets: 2/2

Experience can be found in green vials throughout the level and in enemies that you kill. Be sure to grab all the secret chests along the way, while they do not break down per level like the experience does "Treasure Hunter" will pop for you when you retrieve the last chest.