Cosmo Rules is the thirty-third episode of Season 7.
In this episode, after Jorgen Von Strangle gets the trick-ups (bouts of hiccups followed by bouts of cheesy magician-like trick magic), he's unable to enforce Da Rules, but only another relative of the Von Strangle family can do the job. As his Nana Boom Boom, who was playing Explosive Bingo, and his invisible cousin, Leonard, who was in the Bahamas, are both unavailable, Jorgen's closest available relative to enforce Da Rules turns out to be Cosmo (Nana Boom Boom explains to Jorgen that Cosmo and his family are actually distant relatives of the Von Strangle family).
At Fort Jorgen, Jorgen has completed another successful day of enforcing Da Rules and preventing fairy god-kids from wishing up total chaos. But when he drinks a can of Fizzy Juice, he gets the trick-ups, which are like hiccups, but laced with uncontrollable magician-like trick magic. This instantly changes his attire to that of a magician, before creating a bomb that destroys Fort Jorgen. Finding that these magic tricks are beyond his control, Jorgen pulls the "Conveniently Placed Family Locating Lever" to find the nearest Von Strangle to carry out enforcing Da Rules, which poofs him to Timmy's bed. He asks Wanda to lends him the video-phone and they call Nana Boom Boom, who is playing Exploding bingo; Timmy comments, "That's some freaky bingo."
Jorgen asks his Nana why the family locator lever took him to Turner's house. Jorgen concludes that it must have been broken, but Nana Boom Boom tells him there is another Von Strangle in the room with him. At first, Jorgen thinks that it's his invisible cousin Leonard, only for Nana to say that he's in the Bahamas. "But, say hello to your, more deep, dark, family secretish cousin, COSMO!" Shocked at the prospect of being cousins, both Jorgen and Cosmo cry "NOOOOOOOOO!" for a day, but it turns out Cosmo was saying "No way!" Jorgen, on the other hand, faints and wakes up, thinking the whole trick-ups and Cosmo being his cousin was just a dream. However, Cosmo corrects that it was really a dream come true for him. Refusing to believe it, Jorgen poofs up his family tree, where Cosmo finds himself on a broken, withered branch at the very bottom.
As much as it pained him to say it, Jorgen passes responsibility of Da Rules to Cosmo until he's better. Simply, Cosmo has to enforce whatever's written in Da Rules. After passing his wand to Cosmo, the trick-ups cause Jorgen to cuts his own body in half, so Wanda & Poof take Jorgen to Fort Jorgen, to help him heal. Cosmo dresses like Jorgen and attempts to be like him, but Timmy writes on Da Rules with a crayon that Timmy is allowed to break the rules, and Cosmo irresistibly approved it, although there is one of Da Rules which says that fairies can not argue with official-looking green crayon, because their godchildren will break any of the (other )rules, especially when they use green crayon to do it. So Timmy wishes he had aton of money, he won a number of competitions and Trixie Tang fell in love with him, so he could become popular.
At Fort Jorgen, Wanda tells him he can heal himself by drinking lots of water, so Poof fills the room with water. It doesn't work as Jorgen tricks-up a fish and a swordfish. Back at Dimmsdale, seeing that Cosmo isn't going to allow any other kid from being unrestricted by Da Rules, so Timmy writes in the book that no godkid has to follow any of Da Rules. So the rule is on and Chet Ubetcha quickly catches on that various kids have their wishes for money, winning competitions and love coming true also. Unfortunately, there is a drawback, as Da Rules starts fracturing and spilling out magic beams that plunge the world into chaos.
Meanwhile, Wanda tell Jorgen another way to heal is by scaring him, so she turns into a scary monster but nothing. The trick-ups then cause the Statue of Liberty to appear in the Turners' living room. Jorgen says he is too worried to be scared, and Wanda tells him that as the universe is not falling apart, it means Cosmo is doing a good job, but then Jorgen's Universe-Is-Falling-Apart Siren sounds. They quickly poof back to Timmy's, where they find the world in chaos. Jorgen accuses Cosmo of being a bigger moron to have cause this. Cosmo defends that as he's still the same size moron and secondly, he doesn't even know how this happened. Timmy admits that he altered Da Rules so that there were none. Shocked at what he has done, Jorgen says that without rules, every rule-free wish destabilizes the book further. And worse, if it explodes, that means the universe will too. The only thing that can fix the book is a Von Strangle, but Cosmo is too weak to do it, so Jorgen's legs and the rest of his body and Cosmo try to assemble the book, and Cosmo can't take it anymore, and Jorgen tell him that he can because he is a Von Stangle. Cosmo gains strength from this and the book is fixed. Wanda, Poof, Cosmo, and Jorgen then scold Timmy for his selfish actions. Timmy is then forced to play Exploding Bingo as punishment for nearly making the universe fall apart, literally causing him to blow up.