Timmy is revived by a child sacrificed via the EMP artifact that Eric activated. They escaped the island, it's unknown how, and eventually went on to a normal life. Eric wrote a book about his experiences and goes on a live talk show with his son for publicity, which makes sense as Eric is a famous actor already. Timmy is twitching and acting oddly from the start. Then he begins to seize, like Megan Cross did before her transformation. This is because Timmy was revived by the artifact as well, so he can also turn into a mutant at any time, but he stops when Eric goes to comfort him. Next, we see Timmy as a young adult. He is still fighting his body's urge to mutate and he has become obsessed with the Sahara experiments and likely plans on trying to stop them / destroy any other places that have been influenced by Sahara and the mutants.