Mr. Mopsey is a stuffed toy cat belonging to Numbuh 3. Its first and only appearance is in Operation: L.I.C.E. Mr. Mopsey is implied to be one of Numbuh 3's favorite stuffed animals, due to her carrying him throughout the entire episode.
- In Operation: L.I.C.E., Numbuh 3 mentions having other favorite stuffed animals as well, the others being Mr. Winkle Snob, Marry Pizza Face, Little Roosey Mockleupadis, Little Pepe Pie, and Mr. Dinkle Doo.
- Apart from her Rainbow Monkeys, Numbuh 3 is only known to have given names to these stuffed animals.