Diablo II Item Drop Procedure

Order of drop calculations is fairly close to this:

• check monster type (normal, champion, boss/minion)
  • if boss monster or minion, generate treasure class listing with +3 monster levels
  • if champion monster, generate treasure class listing with +2 monster levels

• check max treasure class of monster and roll for drop (tc 87/arm87 would be max for the game) yes/no?
  • if no-drop, go to next lower available TC and roll again (repeat till item treasure class is selected or no-drop in TC 3 or lowest available treasure class)
  • if act boss monster, repeat check for each possible item drop untill no more checks remain

• check dropped item for unique drop yes/no
  • Check to see if item already dropped in this game, either as a failed unique or as a unique item, or generated as an item in the gamble screen if item not already generated, continue, if no, drop 3x durability rare item
  • check if there is currently a unique available for this item, if yes, continue, if no, drop 3x durability rare item
  • check qlvl of unique item vs monster mlvl (qlvl < mlvl), if yes, then unique item drop allowed, if no, drop 3x durability rare item

• if not unique: check for set drop yes/no
  • check if there is currently a set available for this item, if yes, continue, if no, drop 2x durability magic item
  • check qlvl of set item vs monster mlvl (qlvl < mlvl) if yes, then set item drop allowed, otherwise drop 2x durability magic item

• if not set: check for rare drop yes/no

• if not rare: check for magic drop yes/no
  • if random boss monster, force magic item drop (doesn't apply to runes, potions, scrolls, and other items that cannot be magical)
  • if act boss monster, force magic item drop (doesn't apply to items that cannot be magic, again)

• if not magic: check for superior (mf not applied after this point) yes/no

• if not superior: check for normal quality yes/no

• if not normal: check for inferior yes/no

• for all drops: check for ethereality
  • set items cannot be ethereal, the ethereal flag cannot be set
  • rings, amulets, and charms cannot be ethereal, most of them do not have an ethereal flag to be set, some exceptions exist
  • The Stone of Jordan is always ethereal, the Annihilous charm is always ethereal, the Hellfire Torch is always ethereal, the Gheed's Fortune is always ethereal (all of these items will disappear instantly if sold to any vendor, without any possibility of purchasing it back at ANY price)
  • inferior items cannot be ethereal, the ethereal flag cannot be set

After all is said and done, a pseudo-random item is generated out of a monster's possible droplist. Not all monsters in a given area use the same TC droplist ... some monster types are simply not allowed to drop items from certain treasure classes, while others in the same area can... Listing which monsters can drop from what treasure class would be extremely tedious and space consuming, so I wont do that here. As you can see, the process is indeed somewhat complicated, but after you get the theory behind it, it gets a lot easier to see where it's going.