in almost every episode, dr. doofenshmirtz builds a machine called an inator either to get revenge on someone from a backstory or to take over the tri-state area and is beaten by perry the platypus. even though he loses to perry every time, dr. doofenshmirtz accidentally destroys whatever phineas and ferb built that day so that when their sister candace tries to show it to their mother there is nothing there and candace looks like she’s crazy.