5.2 Luck & Chance
Luck is an additional property that every drop can have. It is a number between -2 and 2, inclusive, that indicates how 'lucky' the drop is. This value is used when a Lucky Block is crafted together with valuable items (See 1.3 Luck Crafting) to increase its luck. When a Lucky Block is harvested, the drop it will chose will be based on its luck, and therefore each drop should specify how lucky it is.
The lucky is specified by adding '@luck=X' to the end of a drop. Below is an example that drops a 4 diamonds and has a luck of 1.
Chance is used to specify how likely a certain drop is to be chosen, in relation to other drops. Usually, almost all drops should have an equal chance of occurring. However, it is sometimes appropriate to modify the chance of an exceptional drop, such as one which is extremely lucky or unlucky. The default chance is 1, and therefore a drop with a chance of 2 would be twice as likely to occur. Similarly, a chance of 0.5 would be half as likely, and 0.1 one tenth as likely. Luck is specified similarly to chance, using '@chance=X'. It is irrelevant whether the lucky or chance is specified first, but both must be at the end of a drop. Below is an example of a Wither boss which is both unlucky and unlikely to occur.
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