The Secret of NIMH
Timmy spends most of the first film sick from pneumonia, but all of it in bed, as he hasn't completely recovered yet.
The Secret of NIMH 2: Timmy to the Rescue
In the sequel, he was chosen by Nicodemus to save the rats from NIMH (Which never happen in the books and he was supposed to be the villain. Nicodemus never mention that Timmy was chosen to save the rats from NIMH in the first film). He was first shown in a race with a rabbit and walnut-shell halves with his brother, Martin, until he fell out and took a shortcut, only to land in a trap set by Dr. Valentine. He apologizes to Martin for ruining their last race together, but is sarcastically called "hero" for being the chosen one. Timmy feels that it was Martin who should have been chosen just for being older and stronger, much to the latter's belief. Martin gives him a slingshot and teaches him how to use it. However, when Timmy finally succeeds, he hits Jeremy the Crow on the wing by accident. He is taken by Jeremy to Thorn Valley, and his teachers are Justin and Mr. Ages. They teach him about fulfilling his destiny, even as he ages into a young adult. Then, he meets a young mouse named Jenny McBride, who eventually becomes his girlfriend.
One night, he remembers to "adapt and improvise" (something Justin taught him when he was younger), and saves the rats of NIMH. He even saves his brother, who had become a villain, due to being part of his family. He has finally fulfilled his destiny.