It is a Krabby Patty with its regular condiments, vegetables, and toppings, but with the additional topping of jellyfish jelly, made from the jellyfish of Jellyfish Fields.
Role in episode
During SpongeBob's lunch break, he spreads some jelly on a Krabby Patty. Fred is intrigued by the sandwich and wants jelly on his patty too, so SpongeBob gives him some and Fred loves it.
After Fred tells Mr. Krabs how much he likes SpongeBob's new recipe, Krabs makes it an item on the menu, but he starts bribing SpongeBob to frequently catch more and more jellyfish until there are no more left in the entire city, except No Name.
Mr. Krabs then puts the jellyfish in a large jellyfish-milking factory, where the jellyfish experience some horrible treatments just for the juice they are producing. No Name is angered about this and he later captures SpongeBob and transports him to the factory.
SpongeBob and No Name manage to free the other jellyfish from a large tank inside the factory after fooling Mr. Krabs to say the "open" keyword. Once the jellyfish in the tank inside the factory are released, they attack and sting Mr. Krabs. This forces him to remove the Jelly Patty from the Krusty Krab menu.
Role in SpongeBob Moves In!
They appear as a premium food. It requires one Krabby Patty and a jar of jellyfish jelly, the premium currency of the game. It takes 45 seconds to be made. Thanks to it being a premium item, an NPC wishing for this is rare.
Fred thinks this food tastes so good that he sings a song about it.
There is also a blue Jelly Patty made by Friend, but SpongeBob never eats it.