This Is Your Wish is the eighteenth episode of Season 3.
Mama Cosma pretends to be nice at Timmy and Wanda, by taking them to the Pointy Crown, but it soon turns out to be another plot for her to get rid of Wanda. Only this time, it takes place in a game show with Billy Crystal Ball, and an audience who will judge Cosmo for his past actions to decide if he is fit to be a godparent. If the audience votes against him, Cosmo will be sent back to his mother, separating him from Timmy and Wanda.
Mama Cosma surprises Timmy and his Fairies by inviting them to a dinner at the Pointy Crown, a restaurant so fine that Jorgen, Santa, and the Sandman have all eaten there. Naturally, Wanda is suspicious, and so is Timmy. At the fancy restaurant, Cosmo and Mama Cosma are given an exceptional table, while Timmy and Wanda are given one of the worse table (right in between the doors for the bathroom and the kitchen's out door, resulting in Timmy and Wanda continuously getting smacked in the head by the doors). While there, the four are surprised to find Billy Crystal Ball there. He seems to be interested in Cosmo and eventually reveals a surprise; Cosmo has been brung to the restaurant to reunite with his past acquantances and take a stroll down memory lane on the show This is Your Wish. This only leads Timmy and Wanda to become even more suspicious, only to get smacked by the doors again, resulting in Wanda saying she has a slight concussion and asking if Timmy's pink hat had always been orange
While on the show, Cosmo is greeted by people he knew from past disasters, rather than anything fun. The first person who greets him is Mama Cosma. She tells the audience of Cosmo while he was a baby to a toddler. When Cosmo got his first wand, Cosmo immediately turned his father into a fly. When Cosmo turned five, Mama Cosma put him in art classes. Instead of painting, he cause an explosion that took out half the class while making an exploding daisy. When he was eight, Mama signed him up for sports. Unlike the other fairy children, who turned their disks into cute creatures, Cosmo turned his into a fire-breathing dragon named "Snowball".
The next person to re-live memories is Jorgen Von Strangle. It is revealed that Jorgen was Cosmo's 5-Star fairy commander while Cosmo and Wanda were at the Fairy Academy. While there, Cosmo caused a number of disasters; During his first day of sixth grade, during a salute, he turned a bird into "Snowball". He repeatedly summoned this destructive dragon, which always caused fires to break out. Jorgen sentenced Cosmo to clean toilets for the rest of his days at the academy. But as Cosmo grew, so did the chaos he carried with him. During 7th grade, he destroyed the shiny utopia of Pompay by causing the volcano to blow; During his freshman year, he sunk the sparkling utopia of Atlantis; During his sophemore year, he turned the high-tech utopia, Xanadu, into Pittsburgh. Jorgen cuts the memory when rage and vengeance overtakes him. He rips off his tuxedo with one big flex, but just before he can cause Cosmo any harm, he is shot in the butt with tranqualizers and carried away.
The audience cannot believe the chaos that Cosmo caused, and are glad that they will be able to vote him to stay home under the care of his mother. Timmy and Wanda realise this plot and decide that Mama Cosma must be stopped. Fortunately, Wanda is the very next person set to re-live memories. She tries to tell the audience about Mama's plot, and attempts to show footage of Cosmo doing amazing and heroic things. Mama, however, battles Wanda to show how destructive Cosmo is. Wanda continuessly shows clips of Cosmo saving their lives, while Mama shows clips of Cosmo endangering their lives. In the end, it turns out Cosmo is too much of a danger. Timmy decides to show his clips. Two of these clips, while showing Timmy as being happy, show Wanda as constantly being in danger. These include Wanda almost being eaten by a giant, hungry spider and Wanda being set on fire. This all results in Timmy's--and the audiences—enjoyment. Timmy tells them that while Wanda is the responsible one who gets them out of trouble, Cosmo is the fun one who makes Timmy laugh. This still isn't enough to convince most of the crowd, however, Timmy reminds them all that if they vote for him to stay, then he would be in Fairy World with them with more disasters to come, scaring them into making Cosmo stay with Wanda and Timmy. In the end, Cosmo summons Snowball once again.