In the beginning, he stole the Majora's mask from the happy mask salesman. He put it on and the mask took over his body, skull kid was link friend, and after he defeated majora. Link and him became friends again. Right now he is walking next to you (link) and you guys are laughing and joking.

"Link!" "Look over there!!" He exclaimed

"What is that?" You ask

"I don't know let's check it out!" He yells excitedly

You hop off epona and run after him as he runs to what he saw.