Seth Nelson was a student of Smallville High School and a metahuman with the ability to control magnetic fields. He was the main antagonist of the episode "Magnetic" in the Third Season of Smallville.
Seth Nelson was the lab partner of Lana Lang, whom he's had a crush on since sixth grade. Seth worked at the Smallville County Fair as a booth operator where he gave out prizes that were snow globes of Smallville with bits of meteor rock in them. He saw Lana with Chloe Sullivan and offered her a free try to win a snow globe. Lana misses completely and Seth tries to give her a prize anyway, but another patron was offended and starts a fight. Seth ran away, but the other patron found him and bashed him over the head with a snow globe. Seth was knocked down with a gash on his forehead and tiny bits of meteor rock enter his blood stream.
At the hospital, Seth received an MRI which acted strangely with the meteor rocks as the magnetic field reacts badly with the Kryptonite in his blood. The machine shorts out and shocks Seth which gave him magnetic powers that influence both metallic matter and mind. Lana rushed into the operating room concerned for him and when he touches her hand, tiny green sparks appear, and Lana suddenly finds Seth attractive. The next day Seth realizes he can control metal objects without touching them. Clark and Lana visit Seth together, and Seth asks Lana on a date. She is reluctant at first, but when he touches her hand, she agrees as a suspicious Clark looked on. When Seth came to pick Lana up, she tells him that she can't go out with him, but when he touches her, she suddenly changes her mind.
For their date, Seth took Lana to the carnival after hours using his power to open the gate. Lana was amazed but not scared and they ride the Ferris wheel together. They ride the Ferris wheel together. Clark has followed them, and when he hears Lana laughing, he thinks she's screaming, and pulls the Ferris wheel to a stop. Lana and Seth are annoyed that he is "stalking" them, and leave.