Luck

What is luck?
"'There are some things you need luck for, otherwise you won't really go anywhere.' -Gambler"Luck increases the likelihood of various items or enemies yielding better rare item drops, or in the case for items which can have a negative outcome, it has a greater chance of being a positive one.

$$Chance \times Luck + (LuckBoost \times LuckMultiplier) $$

What positively affects the Luck Multiplier?
Unlike normal luck, which can stack with other things, only the highest Luck Multiplier will apply.