It is a Krabby Patty with its regular condiments, vegetables and toppings, with the addition topping of Jellyfish Jelly, made from the Jellyfish of Bikini Bottom.
During SpongeBob's lunch break, he spreads some jelly on a patty. He gives some to Fred and he loves it. After Fred tells Mr. Krabs how much he likes SpongeBob's new recipe, Mr. Krabs makes it an item on the menu. But he started bribing SpongeBob to catch frequently more and more jellyfish, until there were no more jellyfish left in the entire city, except No Name. Mr. Krabs was then putting the jellyfish in a large Jellyfish Milking Factory, where the jellyfish experienced some horrible treatments just for the juice they're producing. No Name was angered about this, and he later captured SpongeBob and transported him to the factory. SpongeBob and No Name managed to free the other jellyfish from a large tank inside the factory, after fooling Mr. Krabs to say the "open" key word. Once the jellyfish in the tank inside the factory were released, they attacked and stung Mr. Krabs. This made him remove the Jelly Patty from the Krusty Krab menu. The Jelly Patty was not seen in any other episodes since.
SpongeBob Moves In!
Jelly Patties appear in the game, SpongeBob Moves In!, as a premium food, it requires 1 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.