Question

why was the first game complicated for Michael

Answer 1

because he was confused he was thinking that the boy was real or not 

Answer 2

A new character had suddenly made an appearance amidst the game and was trying to command and help Michael in the game. There was a new twist to the game with the entry of the second sheriff. Earlier, Michael was the only sheriff in the game and thus things seemed easy to him, he understood that it was a usual game about a fight between the hero and a villain.