It looks like a regular pie. It has magenta filling that is made with seaberries.
Role in episode
A fish brings his grandma's favorite seaberry pie to the Krusty Krab. Squidward suddenly comes flying at the pie and smashes into it, and since he is allergic to seaberries, he puffs up. Patrick thinks that he is a monster who is going to attack SpongeBob, so Patrick attacks Squidward.