This Is Your Wish is the eighteenth episode of Season 3.
When Cosmo becomes the contestant on Fairyworld’s most popular game show, Timmy and Wanda discover it’s just a plot by Mama Cosma to get him away from them. With the help of some video clips of Cosmo’s past, Timmy tries to stop the audience from voting Cosmo back home forever.
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 tables (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 brought to the restaurant to reunite with his past acquaintances 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 caused 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 three-headed hydra 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 a salute on his first day of sixth grade, 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 Pompeii by causing the volcano to blow; during his freshman year, he sunk the sparkling utopia of Atlantis; and during his sophomore 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 tranquilizers 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 realize 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 continuously 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 audience's — 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.