Dark Reflections: Spectres is a sourcebook on Spectres for the old World of Darkness “Wraith” game. It’s on the now-defunct “Black Dog” label, which was White Wolf’s publishing venture into more “mature” material.
Spectres in Wraith (and Orpheus) are very nasty critters and as close to real “evil” as these games really get. The hollowed-out shells of people (and things) who have (often willingly) given themselves up to Oblivion, they inhabit the Labyrinth and wreak havoc in the Shadowlands in general. They are pure antagonists, in almost all cases, being cruel, vicious, nihilistic and sadistic in equal degrees.
…but not necessarily in all cases. This book gives you some insight into their “culture” (if you can call it that), and provides rules for creating Spectre player characters. As the book notes, this would probably be a short, self-destructive campaign, but it might be interesting. Hard to pull off successfully, in any case.
Most GMs (me included) would use this to flesh out Spectre NPCs, of course. “Evil” beings who are cartoon evil aren’t half as convincing as ones who have a motivation and at least some sort of back story. There are some neat ideas here, though not all that much really new – and the rules crunch is for the old WoD ruleset, which might not be all that useful nowadays. I might use some stuff from here if I even get around to running Orpheus, even though that game has a lot of self-contained material on these sorts of critters and doesn’t really need this.