Rare Drops
Drops marked as SR denote items which have a very low drop rate in a particular mission. Drops marked as SR may show up in higher difficulty missions later on at a higher drop rate.
Drops marked as UR denote items which have an extremely low drop rate in a particular mission. Drops marked as UR may show up in higher difficulty missions later on at a higher drop rate.
The drop rate for UR items is lower than the drop rate for SR items.
To view a list of drops and locations where SR/UR drops can be found, you can use the What Links here functionality: