Discordianism's two best-known contributions are a joke about pattern recognition and a technique for spreading confusion, and both turn out to be making a serious epistemological point.
The Law of Fives
The Principia Discordia states that all things happen in fives, or are divisible by five, or are somehow directly or indirectly related to five. It then notes that the law is never wrong, and invites the reader to work out why. The answer is that a sufficiently motivated observer will find fives everywhere, and that the demonstration of the law is a demonstration of confirmation bias performed on the reader rather than explained to them. It is a better teaching device on the subject than most textbook treatments, because the reader supplies the evidence themselves.
Operation Mindfuck
Attributed to Kerry Thornley and Robert Anton Wilson, this was the practice of seeding contradictory material into the culture: letters to magazines under false names, planted rumours, absurd conspiracy claims issued alongside real ones. The stated purpose was to make people notice how much of what they accept arrives without provenance. The Illuminatus! trilogy is the largest artefact of it, and the modern circulation of the Illuminati as a conspiracy staple owes a great deal to a campaign whose point was that such stories should not be believed.
Where the joke stops being one
The material has been taken literally often enough to matter, and some of what it seeded is now repeated in earnest by people who have never heard of Discordianism. Whether a religion that cannot be distinguished from its own parody is a religion is a question the tradition asks about itself and declines to answer, which is consistent.