While your voice itself is good, you didn't quite match the tone needed for the lines. First two lines would have a bit more severity in his voice. Joker, the worst of the worst has come back, Nightwing knows how dangerous he is and that Batman needs support. I know act laughing is a hard thing to do (which is why it's a autition line because it's important scene). I would have to be blunt and say that your laughter seemed slightly fake and way too light considering that Grayson and the rest of the Batfamily have been hit by Joker's laughing gas. He is trying to stifle maniacal laughter, so it must sound aggressive and loud. Near uncontrollable.