Slaadi are batrachian ultraterrestrials (or Outsiders, in D&D-speak) devoted to pure chaos, immortalized in AD&D's Fiend Folio. They were the creation of science-fiction-writer-to-be Charles Stross who describes their creation as "an independent exploration of Lovecraftiana"--since he wouldn't actually discover Lovecraft until "a couple of years later."
To keep slaadi interesting, here are nine (maybe) little know facts (some of which are untrue. Probably) to inspire their next foray to your Prime Material Plane:
1. There are no slaadi--or at least there weren't. Perception of them is an artifact of sentient minds interacting with the absolute, unfiltered chaos of Limbo. Unfortunately, the substance of limbo is psychoactive and has likely began to spontaneously generate slaadi under the deformation of visitor expectation.
3. The skin of slaadi produce a susbtance (slaadslime) which if ingested by sentient beings expands their perception so that they may perceive the intersections of planar forces on the Prime Material Plane. Or, alternatively, it may just cause users to hallucinate that they can do so. Either way, slaadslime has a street value.
6. The minds of the insane or the intoxicated are portals by which the slaadi can enter the material plane.
II. Ssendam, the Anarch of Madness, was created in the mind of a poet--deranged by drugs and syphillis--on some alternate material plane. Ssendam slipped from the poet's delirium and emerged into actuality in the roiling chaos of Limbo. The other slaadi are but cells in the body of Ssendam.
5. Slaadi are all silopsist who believe everyone else in existence is merely a production of their admittedly addled minds, and react to these presumed hallucinations with varying degrees of irritation.
Eight. The sickle of Ygorl, Anarch of Entropy, was "lost" on the Prime Material Plane. It passes randomly from person to person, but its every use, no matter how seemingly inconsequential, works toward the heat death of the universe.
4. Slaadi are the detritus of the gods' revision of the previous mulitverse. Their chaotic nature is due to their substance being fundamentally incompatible with the operating parameters of the multiverse in which they find themselves.
Slaad. Slaadi will exchange gold or magic items for things like yarn, boot-laces, or a cracked ceramic mug, which they often treat as possessing great value. Alternatively, they may just kill the would-be trader.
C. Enigmatic, but nonsensical graffiti found in odd places all over the prime material plane is actually part of slaadi incantation designed to absorb the plane into Limbo.
9. The word "fnord" is used frequently by slaadi, but no one seems to have been able to guess its meaning, and slaadi do not explain, if they even can.