For completing Illusen Quest 20+ you get a pretty avatar.

But you must know something before trying to get the avatar. The items are randomly selected by rarity. So be ready that it could expensive or cheap...from 100np to 100k.

The list of items
Level 1: Illusens Cream Cookie
Level 3: Illusens Potion
Level 5: Illusens Comb
Level 8: Cucumber Eye Cream
Level 11: Illusens Novel
Level 14: Mud Mixture
Level 17: Flower Cake
Level 20: Rain Water Shampoo
Level 23: Rose Shake
Level 26: Earth Spell Book
Level 29: Leaf Shield
Level 32: Illusens Earth Potion
Level 35: Honey Potion
Level 38: Illusens Scroll Level 41: Illusens Blade
Level 44: Leaf Taco
Level 47: Illusens Orb Plant
Level 50: Illusens Staff