According to Mary, it's a key that can open any door (or lock) anywhere anytime. When the key gets close to a lock, it analyzes the lock, changes to the exact shape of the lock's key and opens it.
It only appeared in "Johnny's Keys To Success". The test twins made it and gave it to Johnny to test it. but first warning him to not take it too far,which unfortunately he did by using a closed amusement park and stealing from a bank's safe. When the clips of Johnny and Dukey and how did they used the key to get to everywhere (from the security cameras) got on news, every person in porkbelly attacked the Test house in order to claim the key. the test kids ran to the Porkbelly's military HQ, asking from the General to help but he also wanted the key from them, Johnny unknowingly released a giant robot made by the military scientists by pressing a button (which the robot's goal was to destroy the Test house if they ever invented a bad thing), the crew get themselves to the Test house and Johnny managed to use the same key in order to shut down the robot before it hurts Hugh (who was just cleaning the lab). after the event, the general took the key from the girls in order to destroy it so it won't cause another trouble, which soon was revealed that he didn't destroyed it and instead, he and agents black and white used it the same way that Johnny did before.