When going inside Ice Ring Isle for the first time, uncover the Iron Boots then walk past the blowing wind. You will find a hole. Go inside it. You will see a number of enemies frozen. Do not unfreeze them. Just unfreeze the Knight. After killing the Knight, he will give you a Knight's Crest. Leave the hole , then go back down. The Knight will be there, frozen again. Unfreeze him, and kill him, get another Knight's Crest, and repeat as many times as needed.