The Beast is the main antagonist of Stuart Little 3: Call of the Wild. She is a cougar who threatened to eat the animals if they didn't bring her offerings of food.
Towards the beginning of the film, Reeko showed up without any tribute and bought his way out with a promise of bringing double his quota next time. When the time came and he had nothing to show for it, he conned Snowbell into going to fill his debt. When the Beast noticed Snowbell's thick, luxurious fur, she decided to make a rug out of him so she'd have something warm to lie on during the winter. She only refrained from eating him when he suggested she fatten him up first to have a bigger rug.
When Stuart learned that the Beast had Snowbell prisoner, he set out to rescue him. Later, with the help of Reeko and the other forest animals, he succeeded in trapping her, whereupon she was sent to the zoo. She was likely ill-received there, as the chopper pilot who took her noted that they would have to tranquilize her and shave off her fur to get rid of Reeko's spray.
- The Beast has a lot of similarities with Zira from The Lion King II: Simba's Pride.
Beast was apparently mentioned by Stuart when Beast was donated to died in the forest.