It looks like a Krabby Patty, or any other burger, but gigantic in size. The amount of meat in the patty is so great that most normal spatulas cannot flip it.
Role in episode
It only appears in the episode "All That Glitters." Squidward says that no one has ordered a Monster Krabby Patty in ages. When SpongeBob tried to flip the patty, Spat was broken in half, and it was taken to the hospital. When Spat is cured, another customer ordered a Monster Krabby Patty but Spat (SpongeBob’s Spatula) did not break, but instead SpongeBob's arm broke off.