No Substitute For Crazy! is the thirty-fourth and final episode of Season 5.
After Mr. Crocker suffers an on-the-job injury, Timmy Turner's class has been assigned a substitute teacher named Ms. Sunshine, who seems very nice until Timmy wishes for her to be his permanent teacher. It turns out that she is even worse than Mr. Crocker, and she is really an expert fairy hunter named Ms. Doombringer.
It was only a few minutes left before dismissal and Timmy was hoping that Mr. Crocker doesn't give a pop quiz but Cosmo reminded him. Timmy tries to stall him, and said that he's going to pass the pop quiz. The teacher noticed that Timmy's going to pass the pop quiz, and then spazzed out once again. Mr. Crocker spazzed out about Timmy Turner's fairies a little too hard, he fell out of the school window and into a freshly dug well, causing him to break his "failing hand". The bell went and everybody went home.
The next day, Principle Waxelplax had introduced a new teacher named Ms. Mary Alice Sunshine, will be their substitute, until Crocker's bones got healed. Ms. Sunshine is overly cheery and nice, passing her students even if they make mistakes, and awarding them with gold stars for the most trivial tasks such as going to the bathroom, and even bullying other kids. When it was time for her to part ways so that Mr. Crocker could return to teaching much to the dismay of the students, Timmy wished for Ms. Sunshine to become their permanent teacher. POOF! The next day after that, Timmy saw Mr. Crocker as a crossing guard with an injured arm. He explained how Mrs. Sunshine stole his job and the school board did not trust him in his accident.
At school, the substitute screeched her finger nails on the chalkboard. She quickly revealed her true intentions. She told her students to call her by her professional name, Ms. Doombringer, and that she knew one of her students had a fairy godparent because her gold stars had detected magic. While scanning the students with a magic detecting wand, the school bell rang and her students were released. Ms. Doombringer held Timmy and his closest friends in detention regardless; her magic stars having detected the magic on his friends because it rubbed off on them from being around Timmy so much. She explained to Timmy that she goes to unsuspecting schools, plays nice to the students until one wishes for her to be permanent, in which she knows that a fairy was at work. And when she asks which of them has a fairy godparent, she said she will rip apart its wings and crown.
While being distracted by the school lunch bell, Timmy and his friends momentarily escape Ms. Doombringer, but she corners them with throwing purple stars. Timmy and his friends escape to the bathroom, to which Ms. Doombringer must oblige. There, Timmy paints a Cosmo-face on Elmer's boil, and has him run down the hallway throwing pencil shavings made from Cosmo in pencil form. Elmer runs past Doombringer, who can smell the magic from the pencil shavings, and gives chase to him, allowing Timmy to use sneak past and use Crocker's locker to enter the Crocker Cave. By the time Timmy gets to the cave though, Ms. Doombringer had already found out Elmer was a decoy (his boil got caught in a revolving door), and had him cornered again. She hears Cosmo sneeze, sees Wanda looking annoyed at him, and realizes Timmy's writing utensils are his fairies, but the young lad continues to deny this and runs away.
Timmy manages to exit the school, but he cannot get across the busy city street. Ms. Doombringer is about to catch up to him, when Mr. Crocker, now working as a cross guard, uses his sign to stop the cars and allow Timmy to cross. Ms. Doombringer tries to cross after him, but Crocker changes his sign to allow the cars to go, causing Ms. Doombringer to get hit by a school bus. She is last seen stuck to the front of the bus as it drives away, vowing to someday return.
Timmy says thank you to the Teacher/Traffic warden, but when Crocker decides to give him a gold star, the young boy flees, leaving Crocker no choice, but to hold the green sign.
The day after the next day after that, Mr. Crocker comes back with pop quizzes. When Timmy's ready, Crocker felt so uneasy with the whole FAIRY GODPARENTS situation, he jumped his head into the lights and then got electrified. Principle Waxelplax announced "Bring in the new substitute", who is actually a Monster Hunter. Timmy turns to the innocently whistling monsters behind him and tells the Dracula-type kid: "You might want to get out through the cave." as the episode ends there.