Who is this Master Lee who comes at the right time to help Uk-Mudeok?
My theory:
He knows it all. He's lived for a long time, and maybe searched a lot for the ice stone. He also knows Mudeok is helping Uk.
I think:
Master Lee asking Uk to be his student, he will train him to be strong and UK will intern help Naksu get her powers back idk how ..but then Mudoek might have the ice stone.
Master Lee can then obtain the ice stone from them, and seal the ice stone once and for all.
Master Lee's goal according to my theory: Help Uk and Mudoek, get the ice stone, seal it.
End of ice stone and Alchemy of Souls sorcery story