The World Born Dead
The shadar kai are shadow fey from the plane of Shadow. The race is from the 3.0 fiend folio.
Look it up, if you interested. What? Do I have to post everything? Okay. Fine. They are ECL 4 creatures which means a level 1 Shadar kai rogue is the equivalent to a 5th level character. They get a +10 racial bonus to hide in shadows, they can hide in plain sight, and yes, they are proficient in the spiked chain.