Obsidian candles: disposable single use item to be used in Infernally tainted rituals granting a small bonus (up to +5) to the casting total.
They are not obviously evil, and at first the party can be asked to provide some for an older weirder mage who blames a disruption in shipping from Anatolia (but actually wants to keep this on the quieter side and not order them through Red-Caps). A while later, having completed the quest, the party discovers a half dozen obsidian candles in an infernally tainted area or even an Infernally fallen Covenant (like Rudiara).
Not a big world ending device but something to use as a springboard.