Allows you to make potions of luck (and unluck) in survival, the level of effect will also stack with any looting or fortune enchants.
Having luck II while mining with fortune 3 will act as fortune V, while having unluck II would act as fortune I.
To brew potions of luck, break tall grass to obtain a lucky clover(1/200), clovers are also compostable.
However, to brew a luck II potion you must add a rabbit's foot, to which you can then add glowstone dust for luck III.
Adding a fermented spider eye at any point will make an unluck potion.
If you wish to port to fabric, feel free to use my source, this just came about from a much larger project I'm more focused on.