For one thing, Joshua can levitate, so anything Shadow tries to do he can just avoid.
Second, one of the game's cutscenes shows that Joshua can stop things moving in midair. In the cutscene, multiple bullets are fired at him, and he just made them stop and fall. So, shooting at Joshua would do nothing either.
Thirdly, Joshua can press the buttons on his phone to spawn random objects which he can then fling at enemies. In other words, if Joshua wanted to make a random car appear in midair and then fling it at Shadow, he could.
*Licks finger, touches arse and makes a "TSSSSS!" sound* Beat THAT!!