The FIFA U20 World Cup will be held in Egypt from September 24 to October 16 and the Reds right-back says he and his national teammates can get past the group stage.
"We're aiming to at least get to the next round," Mullen said.
"We're in a tough group but we have the self-belief.
"We've had a lot of tournaments leading up to the World Cup, all the boys know each other and we all know the way we're supposed to play."
Mullen will be joined in the squad by fellow South Australian Ryan McGowan who is playing with Hearts in Scotland but Ryan's brother Dylan along with Rocco Visconte and goalkeeper Mark Birighitti were unlucky to miss.