Each Mystic Eye is located around the Enchanted Kingdom:

Eye One: Pummel Weed is required. Go to the beach by the palace and use Pummel 
Weed's Uproot attack and flip the shells. It is under one of them.

Eye Two: Ash is required. Go to the dungeon. Go straight through the first 
doorway and turn left. Light the torches on the wall and go in the room. It is 
floating in the middle of the room.

Eye Three: Chilla and Major Ruin are required. Go to the Throne Room. Go right 
into the Ancient Tower. Go left along the wall until you see a "quarter pipe". 
Use Major Ruin and go up to the second level. Go to the frozen wall and use 
Chilla to climb to the next level. The Eye is in the middle of the shiny light 
in the middle of the tower.

Eye Four: Thermite is required. Go to the Chamber of Living Portraits. Use 
Thermite's Mortar attack and blow up the Statue Of Thorn.