It works like any other RPG ever made that uses an RNG loot system. The system was created and made popular by the dice-roll system of Dungeons and Dragons. The developer creates the loot table. The loot table is built in a way where a range of numbers is occupied by an item that the developer decides they want that loot roll to comprise of. For instance (just an example): Atheon loot table 1-19 Sparrow 20-29 Shader 30-59 Helmet 60-79 Hezen Vengeance 80-89 Exotic Weapon 90-99 Vex Mythoclast The RNG simply does what it's called, and generates a random number between 1 and 99. Whichever that number is, is the item that you get depending on how the loot table was built. This is a basic explanation of how RNG works, and there can be multiple RNG rolls for each loot roll you perform. For example (let's say at the end of a strike): RNG roll 1 - decides whether you get an item or not (if yes, continue to RNG roll 2. if no, stop here) RNG roll 2 - decides how many item rolls you get (multiples for roll 3) RNG roll 3 - decides the item type you will get (shader, ship, engram, exotic, etc, for RNG roll 4) RNG roll 4 - decides the specific item you finally recieve (return to RNG roll 3 depending on outset of RNG roll 2) Each of those rolls will have a table that has been designed by the developers and can possibly be static or dynamic. Your chance for an Icebreaker in roll 4 may be 5%, but you must consider your chances of even being able to roll for an exotic item in the first place. The specifics of the loot tables in Destiny will obviously only be known to Bungie coders, but knowing those specifics doesn't really help the player base in any way. The only benefit we will have is to quench our curiosity and I'm sure there are countless different loot tables in the game for different mobs/scenarios. I'm sure it's not worth Bungie's time to have to explain those specifics to us.