How does the polymorph spell interact with Emrakul, the Aeons Torn in a game of Magic: The Gathering?

The polymorph spell in Magic: The Gathering allows a player to exchange a creature on the battlefield for a random creature card from their deck. When targeting Emrakul, the Aeons Torn with polymorph, the player would shuffle their deck and put a random creature card onto the battlefield. This means that Emrakul could potentially be replaced by a different creature when polymorph is cast.