Junior, the last end-boss, is the easiest to defeat. It's quite possible to beat him without getting a scratch. You will need to shoot every part of Junior's pudgy body until it turns red which means targeting the head, limbs and even his diaper! During one of his tantrums, when he rips apart the roof and vomits, make sure that you shoot the last morsel of yellow upchuck. (If you don't, Junior's last meal is on you!) When he's all red, shoot the darker leg and give him his final spanking!