The number of drops is dependent on the kind of enemy you defeat. For example, you'll mostly get one Red Satin if you kill a normal Eremite, but the bosses who can manipulate a certain element usually drop multiple Red Silk and Brocad

Sand Grease Pupa is a regional specialty in the Sumeru Desert, and just like every other specialty in the area, Primogems Meta Strategy it's quite difficult to farm .