Spiderwick Chronicles

Once you finish chapter 7..... As Simon find the Hobgoblin (outside the mansion in a tree) he wants you to kill some Bull Goblins by the cypress tree portal in the deep woods... once you've killed them all, go back to the tree at the front of the mansion and talk to the Hobgoblin who will then spit in your eye.... Yummy!
now you can see the magical world without your monocle.

You cannot get this achievement until after completing Chapter 7, and you must be playing as Simon.

First go talk to the Hobgoblin. He's located up in the tree directly out in front of the mansion's front door. He'll give you the quest.

Make your way to the Deep Forest, and then to the large pond with the island and teleporter tree in the middle of it. This area will be infested with Bull Hobgoblins, so kill all of them. Some of them are located on the ground, but many of them are up on top of rocks and cliffs where you can't reach them. Use you tomato bombs or gobstones to get them. Be sure to check your Field Guide and make sure the quest box is checked off before heading back so you don't have to come all the way back here to find one that you missed. I believe the box is marked "Kill Hobgoblins", or some such.

Head back to the house and talk to the Hobgoblin out front to complete the quest and unlock the achievement.