The Secret Patty is almost similar to the original Krabby Patty, except that the sandwich is red and orange colored and levitates a bit.
Role in episode
After hearing from one of the customers about wanting something new, Mr. Krabs hires Sandy to create a new-and-improved version of the Krabby Patty. At first, the Secret Patty turns out to be a success, but at the end of the day, it is revealed to have a terrible side-effect. Whenever someone eats it, they become mutated into Krabby Patty zombie monsters. SpongeBob was the only one who wasn't affected by the patty's effects since he never ate one.
During the chaos, SpongeBob learns that the only cure for the patty's effect is raw chum and saves the day. Once everyone was cured, Mr. Krabs and Sandy decide to never sell the Secret Patty again.
According to the storyboard, the Secret Patties were originally going to be purple.