Spooky Shit

You best not mest with Spooky Shit.

Something that's mysterious and has odd side effects, usually magical or magic-like, that no one should carelessly fool around with as they don't know how it functions or what could happen should something go wrong. The Spooky Shit might come in the form of a potion or strange substance. When Spooky Shit is introduced to a story and the Main Cast is told that it'd be best not to mest with it, the plot says that they should and they later do so.