Cosmo's temporary animal friends are animals that Cosmo got interested in, named, and tried to befriend in Sleepover and Over. All of them except Jimmy were killed
Carl the Ant
Carl was an ant that Cosmo found and named in Timmy's treehouse. Later when Timmy tried to tell his godparents to hide due to his friends arriving, he accidentally shone his flashlight at Cosmo's eye, burning it and causing Cosmo to throw the magnifying glass he was using to observe Carl in the air. The magnifying glass then crushed Carl and Cosmo started crying about his demise briefly before Wanda flew up to and grabbed him, to get him to hide with her. After Timmy's sleepover ended in his friends becoming enemies, he continues crying about Carl's death. At the end of the episode Cosmo cries about Carl again and says "I want my records back!".
Cindy the Bee
Cindy was a bee that appeared near the entrance to the junkyard while Timmy and his fairies tried to come up with an idea to be at both his friends' sleepovers. As soon as Cosmo saw Cindy fly past him, he named her and started chasing her. While Cosmo was chasing her, she was eaten by a bird and Cosmo started crying while saying "Cindy! No-o-o-o! It's too soon!". Shortly after, Cosmo mourned that even though her only knew her for 12 seconds, he'll miss Cindy forever briefly before eventually forgetting who she was while he, Timmy, Wanda were at A.J's sleepover.
Jimmy the Cat
Jimmy is a cat in the junkyard that Cosmo tried to befriend, only to scare him by barking at him. This made Cosmo and Wanda forget the signal on Timmy's plan to get his friends back together (as they realized their sleepovers stunk and Timmy got inspiration from the Major Geek Channel that was on A.J.'s TV). Later, Jimmy was hit by cars after running into the street (and apparently by a horse and a train, given the sound effects), however he survived since he had nine lives and he only lost three in the accidents. He then shredded Cosmo into strips and then stole his dip.