Item Drop Mechanics

Llathias

Banned
Item Drop Mechanics

This very interesting thread was getting off-topic (I blame myself), so I thought we better have another thread.

Item drops is a major subject of discussion here in the SPF. It is being discussed since (probably) the first day, but we're still not challenged to find something new to say. Yet more often, we repeat things that's been said before, either because we can't find it, or didn't read it. This thread is created with the purpose of covering everything about item drops, from /players X command to Magic Find, map seeds to Treasure Classes. Hopefully, we can have the Ultimate Item Drop Mechanics thread, which might be stickied to answer most of the questions about items.

To begin with, can someone, preferably knowledgable of the game codes and mechanics, explain everything that happens from when a monster dies (or a chest clicked) to the moment the item(s) fall on the ground. I've learned some things in this forum, but instead of writing what I think I know and asking the experts to fill the blanks, I'd rather leave it to a D2 mechanics guru to tell the whole story, complete and correct. While explaining, it would be very nice if you could answer the following questions:

  • Why does, for example, Pindleskin have a higher chance to drop a unique/set/rare than a regular Defiled Warrior?
  • What determines which item to drop when there are, say two uniques of the same item type (e.g. Azurewrath/Lightsabre)?
  • What can and what can't be manipulated (legitly, of course) in the item drop/generation process? How is this manipulation possible? (preferably explained with examples and numbers)
  • How does the TC selection mechanism choose a TC, especially between different TCs of the same number (e.g. armor/weapon/rune...)
  • How does the quest drop for act bosses work? Does it narrow the range, hence increasing unique/set drop rate, or make all possible white/blue drops rare without affecting the unique/set roll?

The questions are endless, though I cannot think of any more as of now. If you have any questions regarding item drops, feel free to post them here. If you have the answers, well, we've been waiting for you.

Thank you in advance for making this thread a useful source of information!
 

Thrugg

Diabloii.Net Member
Llathias said:
I've learned some things in this forum, but instead of writing what I think I know and asking the experts to fill the blanks, I'd rather leave it to a D2 mechanics guru to tell the whole story, complete and correct.
We'd rather you did most of the writing and we just filled in the blanks :) Bear in mind I have typed this stuff out dozens of times across many forums. I know I should have just written a guide, but to the chronically lazy (such as myself), answering a few questions a hundred times is easier to confront than explaning a few hundred things, once :) Ah well...

  • Why does, for example, Pindleskin have a higher chance to drop a unique/set/rare than a regular Defiled Warrior?
First and foremost in all drop matters is the file TreasureClassEx.txt. This is zipped up in the MPQ files that come with the game and its subsequent patches. However, due to Atma's need to see this file also, it can be found in your Atma install directory in ATMA_CONFIG\1.10 (or of course the other versions too).

This file governs almost all the drops in the game. A couple of more complicated hard-coded drops happen that aren't in here, but almost all your regular drops are.

If you open it up you will notice columns 5-8 are labelled Unique, Set, Rare and Magic. Any numbers appearing in these columns indicate a bonus to those qualities. Regular monsters, such as the Defiled Warriors, drop from TCs with no bonus. Superunique monsters (such as Pindle) drop with a bonus to Uniques of 800. The way this is calculated into things means that Pindle is 1024/(1024-800) = about 4.5x times more likely to drop a Unique item than a regular monster.

An act boss like Mephisto has a Unique bonus of 983. This makes him 1024/(1024-983) = about 25 times more likely to drop Unique than a regular monster.

  • What determines which item to drop when there are, say two uniques of the same item type (e.g. Azurewrath/Lightsabre)?
As I mentioned in the other thread, the game makes a list of all items of that base type and that quality, which have a level of less than or equal to the monster's level. Levels of unique and set items can be found at www.d2data.net, for example. They are not the same as the required level to wield it, and can not be seen in game.

Each item in the list also has a Rarity value (which you can also see at d2data). There is then an (item's rarity)/(total rarity) chance of each item being chosen to drop. Most of the time there is only one item in the list, and so obviously it has a 1/1 = 100% chance of dropping. When there are two or more items in the list it is more interesting. For example, when Mephisto drops a unique Phase Blade - Lightsabre has rarity 5, Azurewrath has rarity 1. Which means you will get a LS 5/6 of the time and an AW only 1/6 of the time. With rings and amulets there are usually even more choices so smaller odds of each one.

  • What can and what can't be manipulated (legitly, of course) in the item drop/generation process? How is this manipulation possible? (preferably explained with examples and numbers)
Not sure what you mean here. The only number of "yours" that is used is your MF. Other than killing a different monster, there isn't anything much you can do to affect things in a direct way. Well, OK, the players setting makes a difference too, as discussed. That's it.

  • How does the TC selection mechanism choose a TC, especially between different TCs of the same number (e.g. armor/weapon/rune...)
The TCs are like a giant tree, and it is all defined in TreasureClassEx.txt. Each row in that file defines a TC, and lists the sub TCs it can drop from. You roll to see which sub TC you go to, then look at that row, then roll again and so on until you get down to an actual item.

Each sub TC is not equal. For example, Hell Mephisto's TC is
Mephisto (H) 7 983 983 983 1024 15 "gld,mul=2048" 5 "Act 4 (H) Equip A" 52 "Act 4 (H) Junk" 5 "Act 4 (H) Good" 3
This says he gets 7 drops, bonuses of 983 to U/S/R, 1024 bonus to Magic which is why he always drops at least magic.
Next is 15 no-drop.
Then 5 gold with a 2048 multiplier (means decent sized stacks).
Then 52 Act 4 (H) Equip A, which contains equipment items appropriate for the early part of Act 4 Hell.
Then 5 Act 4 (H) Junk, which contains a bunch of crap.
Then 3 Act 4 (H) Good, which contains good non-equipment items appropriate for Act 4 Hell. This is gems, runes, jewels, charms, rings, amulets.

The numbers (15, 5, 52, 5, 3) are the chances of going to each subTC with each drop. They add up to 80. So you have a 15/80 chance of going to no-drop and getting nothing - but that is with each drop. You can go there once and still get your full 6 drops (he gets 7 chances but every monster can drop at most 6 items). 52/80 equipment is why he drops quite so much of that. 3/80 good is kind of low, which is why bosses aren't much good for runes.

Let's have a look at Act 4 (H) Equip A.
Act 4 (H) Equip A 1 weap69 2 armo69 1 weap72 6 armo72 3 weap75 14 armo75 7 weap78 2 armo78 1 Act 3 (H) Equip B 1530
This means you get 1 item, with 2 chances of weap69 and 1 chance of armo69, etc. You also have 1530 chances! of dropping down to Act 3 (H) Equip B.
Several things to note here. First, weapons are always twice as common as armour.
Also, while this is why Mephisto can drop from TC78, he really isn't likely to (especially armour in TC78). Only 1/1566 of Meph's equipment drops will be from armo78, while he is 7 times more likely to drop from armo75.
It looks like he is unlikely to drop from TC69 also, however he drops down to A3(H)EqB almost all the time, and that has a similar TC window shifted one back, ie TC66 up to TC75. So he actually gets quite a few chances to drop TC69 further down the tree.

The main reason why TC3s are so rare is that this rolling window stops when it hits the bottom, so you just get that one very last chance at TC3s.

Suppose you are lucky and you get your 1/1566 chance of armo78 from Meph. This is called an "atomic TC" and it is not defined in TCEx.txt. Instead, it is defined by armor.txt, also in your Atma directory. It contains all armours which have level (often called qlvl) 76, 77 or 78. You can also see base item qlvls at d2data.net. Armo78 contains Balrog Skin, Hellforge Plate, Troll Nest, Crusader Gauntlets and Earth Spirit in 1.10. As always when D2 makes a list, it has rarities associated too. Rarities at this level are pretty simple. All items have rarity 3 except class-specific items have rarity 1, assassin claws have rarity 2, and wands, staves and sceptres (rods) have rarity 1. Armo78 has total rarity 3+3+3+3+1=13, so you have a 3/13 chance of getting a Balrog Skin, and a 1/13 chance of getting an Earth Spirit. Meph is not your ideal source for a Spirit Keeper.

You'll note we split of from runes and rings and amulets a long way back. The game decides if you are getting an equipment item or something else very early on.

By now, we have decided the base item you are getting. Next, the MF process starts, to decide what quality it will be.

  • How does the quest drop for act bosses work? Does it narrow the range, hence increasing unique/set drop rate, or make all possible white/blue drops rare without affecting the unique/set roll?
Right next to Mephisto's TC in TCEx.txt is another one, Mephistoq, meaning Mephisto Quest drop. When you kill him before you have quest credit, you get this one. The only differences are:
Bonuses raised to 993 for U/S and 1024 for R. This means he always drops at least rare, and has a 33x better chance of unique or set than a normal monster.
No gold and no junk. However, the no-drop is still there. Also, this means the total rarity goes down, so the effective no-drop rate actually goes up.

I'd rather answer questions this way if you don't mind. There is so much to it that I'd be here all night trying to cover it all. Ask and I will do my best to answer.
 

Gohanman

Diabloii.Net Member
Nitpick:

Players settings don't affect any individual drop. They just increase the number of drops.

I think Thrugg is *more* correct originally in saying your MF is the only thing that affects item generation resulting from a drop.

EDIT:
Is Meph's 7th drop to allow for the soulstone on his first drop, or do other act bosses get >6 drops?
 

Shakes

Diabloii.Net Member
You can also use the -seed command line parameter that affects the random number generator and hence affects what drops. Although whether that's "legal" or not is a subject of much debate ...
 

AlterEgo

Diabloii.Net Member
Thrugg is da man! :thumbsup:
Shakes said:
You can also use the -seed command line parameter that affects the random number generator and hence affects what drops. Although whether that's "legal" or not is a subject of much debate ...
This will not become a -seed command thread. The FAQ covers it well.
 

Warrior of Light

Diabloii.Net Member
Llathias, I agree with you. We at SPF definitely needs good item drop explanation. May be you could write a guide? I guess we all at SPF will help you with all details. I know a bit about this mechanics, I'd like to help too.
Also RTB and Jurulf usualy in threads, when you call their names. :D

Is it time to rewrite this guides for 1.10?

Magic Find Guide
Item Generation Tutorial

P.S.: Of cause I could do the work myself, I have a bit experience after writing SoJ FAQ, that was published at SC, however I'm bad at English. :(
 

bill_n_opus

Diabloii.Net Member
WoL, i'm more familiar with your old nickname, Igor P (iirc). I remember you used to hang around the Stats forums awhile back.

All you guys should write up a guide and then we can all refer to it.

So we don't obligate Thrugg to write dissertations over and over again. :lol:

That would be a great guide with the likes of Thrugg, RTB, Jarulf (only seen him post very rarely lately), Hakai_no_Tenshi and everyone else, apologies to anyone i've left out.
 

Sumendar

Diabloii.Net Member
Gohanman said:
Is Meph's 7th drop to allow for the soulstone on his first drop, or do other act bosses get >6 drops?
The soulstone is hardcoded, the 7th drop is there to slightly raise the average number of items dropped, as it is possible to get nodrop once and still get the full 6 items.
 

Warrior of Light

Diabloii.Net Member
I have created the table of contents of virtual “Items FAQâ€.

1.Basics
(There will probably be a link or a direct quote of the Arreat Summit)
2.Terminology
(All about Ilvl, Alvl, Mlvl, Rarity and other stuff)
3.Quick Explanation
(a quick explanation of process of item generation after monster killing)
3.1. Number of items
3.2. TC and item type selection
3.3. Item quality
3.4. Item rarity
3.5. Sockets
3.6. Etherealness
3.7. Preffixes and suffixes
(after that is going deep explanation)
4.Game txt data files
(is taken from PK and adopted a bit)
4.1. TreasureClasEx
(by Jarulf)
4.2. Monstats
4.3. Preffixes
4.4. Suffixes
4.5. Weapon
4.6. Armor
4.7. Misc
(+ any other, that I forgot, if needed)
5.Area level and monster level
6.Number of dropped items
7.TC selection
8.Items selection from given TC
(see above at Thrugg's post)
9.Item quality selection
10.Set and unique items selection
(and high durability items)
11. Rarity and item selection
12. Sockets' number selection
13. Affix selection
14. Items generation at shops
15. Gambling
16. Ethereal items
17. Runes and charms generation
18. Quest drops and Andariel bug
19. Non-monster drops
(chests, rocks and other)
20. Countess
21. Crafting
22. Imbuing
23. Cubing
(quote of Uzziah)
24. Circlets and Magic Level
25. Rune making in Hell Forge
26. Magic Finding


Uhhhh! We have quite a bit of topics!

Did I miss something?
 

Uzziah

Diabloii.Net Member
Warrior of Light said:
I have created the table of contents of virtual “Items FAQâ€.
. . .

uhhh! We have quite a bit of topics!

Did I miss something?
I can give you the following sections:

3.5 sockets
12 socket number selection
21 crafting
22 imbuing
23 cubing

They are all in the item manipulation guide.

3.6 Etherealness (this one is easy and RTB has said it many times before)

@Thrugg SHOW OFF!!! :thumbsup:
 

Llathias

Banned
Thrugg: you're amazing!

Warrior of Light: after looking at your table of contents, i realized that i know absolutely nothing about this subject. well, just a bit of TC numbers falling one by one in groups of 4 and Unique/Set/Rare etc rolling one after the other, which everyone else knows. i'd like to write a guide, but you see, i can't put almost anything up myself, and i'm not a good editor. besides, English is not my mother tongue.

although i myself am overwhelmed with the depth and vastness of the subject, an Item Drop guide would be an extremely useful source of data. after all, we have some dedicated people around here (49 guardians/hc psychic hammer sins/10,000 runs...) i also looked at the guide in the battle.net forum, but it's too basic and superficial for me. Thrugg is way bester+1 :p

a few more questions:

we can see magic (blue) items off act bosses in the form of failed sets, right?

as far as i could understand, the Countess has 8 drops in total (3 rune, 5 item). do the last 3 rows mean 2 of those 8 is removed with 1:1 chance of rune/item? if so, why does it have unique/set/rare/magic bonuses? (i most likely misunderstood something here)

i'm not talking about the -seed command, but what is the effect of a certain map on drops (AE: i hope i'm not "crossing the line" with this question). that is, just like people reroll maps to find a Durance 3 entrance close to the wp, would it be logical, or potentially beneficial to reroll maps to improve drops?

when can elite items start spawning? i thought it was Act 4 NM, but found Hyperion Javelins, a Tomahawk and a Pellet Bow while running NM Meph (all from non-Meph sources).

Edit: where can i find (or how can i determine from the TreasureClassEx file) the item drop stats of, say, a Unique/Minion/Champion Moon Lord?
 

Thrugg

Diabloii.Net Member
Llathias said:
we can see magic (blue) items off act bosses in the form of failed sets, right?
Normally act bosses can drop blue items all they want. But, even in quest drops when they are supposed to be all rare or better, yes they can drop blues through it being a failed set item.

as far as i could understand, the Countess has 8 drops in total (3 rune, 5 item). do the last 3 rows mean 2 of those 8 is removed with 1:1 chance of rune/item? if so, why does it have unique/set/rare/magic bonuses? (i most likely misunderstood something here)
Ah, the Countess. Most complicated TC by far. You'll note she has a -2 in her TC row; that means she gets 2 drops but that they are not random, she drops left to right across her TC until she reaches 2. Since her TC contains only Countess Item 1 and Countess Rune 1, it means she drops once from each of those TCs.

Countess Item has 5 drops as you saw. It is otherwise not much different than the other special monster TCs. She has a no-drop of 19 (very important) and gold, equip, junk, good. She will do all 5 of these drop attempts first.

After the Item drop she moves on to the Countess Rune TC. This has 3 drop chances with a simple 5/20 no-drop and 15/20 direct from a Rune TC for those yummy runes. However, remember the 6 drop limit. This isn't a limit on drop chances, just on total drops. If she drops 5 items in her Item drop, she can only drop one more from the Rune (although she still gets 3 chances to do so). Best for us is if she drops less than 5 items from the Item drop so there is room for all 3 Rune drops. Complicated. Only monster where it is actually better to kill her on p1, so nodrop is higher, so Item drops are less etc.

i'm not talking about the -seed command, but what is the effect of a certain map on drops (AE: i hope i'm not "crossing the line" with this question). that is, just like people reroll maps to find a Durance 3 entrance close to the wp, would it be logical, or potentially beneficial to reroll maps to improve drops?
Nothing but superstition except for one thing - racks. Your map seed sets where the walls and doors are on your map but not the monsters. Those are determined by your random stream which is seeded by the clock each time you start up. Except for, of course, permanent fixtures like racks and certain chests. Even those permanent chests aren't affected by the map seed because they drop through the normal TC mechanism which is affected by the genuinely random seed. However for some reason, racks have their item type set by the map seed but the quality determined by the random seed. Hence, rack running. Rack will mostly drop the same thing each time, so you can keep hitting it till you get a unique one. Note this will normally take ~1000 tries. It is almost always faster to get an item just by running a boss.

when can elite items start spawning? i thought it was Act 4 NM, but found Hyperion Javelins, a Tomahawk and a Pellet Bow while running NM Meph (all from non-Meph sources).
The very first elite items are in TC54, the ones you mention plus Giant Conch (actually Pellet Bow is TC57 which Meph can't drop but monsters around him can). TC54 is first droppable by level 54 monsters (it is coincidental that those numbers match, it is not always so) which appear as early as Travincal.

Edit: where can i find (or how can i determine from the TreasureClassEx file) the item drop stats of, say, a Unique/Minion/Champion Moon Lord?
First is to know what TC a creature is suppsoed to drop from. For that you need to look up monstats.txt (again, see your Atma folder). This lists every monster in the game. Find the one you want (can be non trivial because they use tags which are not the same as the display names in game). Moon Lords are bloodlord5, as it happens. Scroll way over to the right end of the row, and you will see a whole bunch of TCs listed. These are, respectively, the TCs dropped by regular, champion and unique versions of the monster in each of normal, NM and Hell.

That's step 1 :) Next, back to TCEx.txt we go. In normal you just look up directly the TC and off you go, but in NM and Hell we have "TC upgrades". This is what the two columns that I haven't explained yet are for - "group" and "level". In NM or Hell, if a monster's level is higher than the level of his base TC, and there is another TC in the same group which is higher level but still equal to or less than his monster level, it will upgrade to that TC.

Suppose you kill a regular Moon Lord in NM Throne Room. His base TC is Act 5 (N) H2H C, group 7, level 62. But he is level 66 because that is the level of the Throne Room in NM. So we look down group 7 until we find the highest TC that is still <= level 66 - which is Act 1 (H) H2H B. So the Moon Lord can drop like a mid-Act 1 Hell creature, up to TC66.
 

Warrior of Light

Diabloii.Net Member
Llathias said:
Warrior of Light: after looking at your table of contents, i realized that i know absolutely nothing about this subject. well, just a bit of TC numbers falling one by one in groups of 4 and Unique/Set/Rare etc rolling one after the other, which everyone else knows. i'd like to write a guide, but you see, i can't put almost anything up myself, and i'm not a good editor. besides, English is not my mother tongue.

although i myself am overwhelmed with the depth and vastness of the subject, an Item Drop guide would be an extremely useful source of data. after all, we have some dedicated people around here (49 guardians/hc psychic hammer sins/10,000 runs...) i also looked at the guide in the battle.net forum, but it's too basic and superficial for me. Thrugg is way bester+1 :p
OK, I have started writing the guide to Item Generation.
Actualy I need just to collect all information about the topics, that I listed in the table of contents.
I will combine all information about it from SPF, Statistics Forum, AB, PK and LL. That is a lot of work. :cheesy:
 

Warrior of Light

Diabloii.Net Member
Warrior of Light said:
OK, I have started writing the guide to Item Generation.
Actualy I need just to collect all information about the topics, that I listed in the table of contents.
I will combine all information about it from SPF, Statistics Forum, AB, PK and LL. That is a lot of work. :cheesy:
The work on preview edition is finished! See it here.
 

Thrugg

Diabloii.Net Member
There was a little controversy regarding WoL's use of material from another site and I expect Elly has pulled the thread until it can be resolved.
 

Warrior of Light

Diabloii.Net Member
Yes, it was issues with publishing here materials from other site(s). I have pushed alarm button and asked to delete entire thread because of copyright breaking. After that the thread has disappeared.

It is nice that I'm still here and isn't banned. :) So I continue my work. At the moment I'm rewriting controversial parts of the guide (there aren't as much copy&pasted information at it as Jarulf thought ;) ).

When the work will be finished I'll post version 0.2 at Statistics Forum again and put the link here.
 
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