It hasn't come to the negative side yet, but I give "-luck" effects to certain items (mostly to the more powerful/broken ones) so they can juggle between a good build and a "lucky" build. But yeah! If their luck stat gets negative it would subtract from their rolls or give them disadvantage!
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The idea is for LUCK to be kinda broken but to use it as inspiration, you get one "manual" use of it per session.
My current campaign is based on Epithet Erased and it has a stamina gauge 1/2
So once I introduce them to the luck system they're gonna have to use their stamina to "change their luck" and depending on the gravity of the situation is the amount of stamina it'll consume!
Also, the creator of EE has a guidebook to run games based on it, it's super fun and relies on improv