The Magic Conch Shell is a light purple toy used by SpongeBob and Patrick to answer their questions. It's only seen in the episode, "Club SpongeBob." It works for both SpongeBob and Patrick (meaning it says "yes"), but not for Squidward.
The Magic Conch Shell looks like a lavender-colored seashell, but has a speaker inside it to help the toy and users can communicate more effectively. It is also operated by a pull-string.
SpongeBob and Patrick would ask it a question, pull the cord, and it would do whatever it said. Squidward asked it numerous times asking to eat some food that SpongeBob and Patrick had, but the Conch continually said no, infuriating Squidward.
The Magic Conch Shell is a parody of the real-world Magic 8-Ball.