Luck is a mechanic that affects most aspects of Zoo.
Your luck is a number stored internally. It functions at any integer, positive or negative, however has a legitimate maximum of 9 (where did this information even come from? citation needed https://discord.com/channels/461575285364752384/1010033674424684625/1060310219038662696) [I don’t think this meant the legitimate maximum, it’s just what was the highest at that time, suggested by Juice Box having no cap] and a legitimate minimum of 0. Luck is stored across promised luck, luck that applies to your next rescue, and additionally your current luck, that is only checked on the rescue itself and not stored.
Luck is obtained in various ways, and provides multiple benefits, such as increased item quality and chances for pairs when rescuing.