Here is Dandylion's comments on the drop rates.

In reference to the drop table of Big Black Dorori :

It's logic is below way.

1. Base

Base Ratio: A (5.5%), B (5.5%), C (5.5%), D (5.5%), E (5.85%), F (5.85%)

It means that you can get a reward item by 33.7% ( A + B + C + D + E + F)

2. When using only Treasure Hunter,

Base Ratio: A (11%), B (11%), C (11%), D (11%), E (11.7%), F (11.7%)

It means that you can get a item by 67.4% ( A + B + C + D + E + F)

3. When using Treasure Hunter + Alibaba

Base Ratio: A (33%), B (33%), C (33%), D (33%), E (35.1%), F (35.1%)

It means that you can get a item by over 100%(202.2%) ( A + B + C + D + E + F)

So Base Ratio is changed as follows for picking a item base on 100%.

Changed Base Ratio: A (16.32%), B (16.32%), C (16.32%), D (16.32%), E (17.35%), F (17.35%)

4. When using Treasure Hunter + Alibaba + Treasure Island,

Base Ratio: A (33%), B (33%), C (33%), D (33%), E (105.3%), F (105.3%)

It means that you can get a item by over 100%, too.

So Base Ratio is changed as follows for picking a item base on 100%.

Changed Base Ratio: A (9.63%), B (9.63%), C (9.63%), D (9.63%), E (30.73%), F (30.73%)

Above calculation is based on 1 item on 1 monster. (item count is independent)

5. For example, when using only Treasure Island,

Base Ratio: A (5.5%), B (5.5%), C (5.5%), D (5.5%), E (17.55%), F (17.55%)

It means that you can get a item by 57.1% ( A + B + C + D + E + F)

6. For example, when using only Treasure Hunter + Treasure Island,

Base Ratio: A (11%), B (11%), C (11%), D (11%), E (35.1%), F (35.1%)

It means that you can get a item by over 100%(114.2%) ( A + B + C + D + E + F)

So Base Ratio is changed as follows for picking a item base on 100%.

Changed Base Ratio: A (9.63%), B (9.63%), C (9.63%), D (9.63%), E (30.73%), F (30.73%)

'Treasure Hunter + Treasure Island' and 'Treasure Hunter + Alibaba + Treasure Island' are the same result on Big Black Dorori.

Each monster's acquirable item list causes the probability to change as above.

I hope the explanation worked to you.

So, what does this mean? Once you get to 100% cumulative drop chance the chance to acquire the item changes!

The equation for calculating this base change when you surprass 100% item chance is:


So in Dandylions original example

When using Treasure Hunter + Alibaba

Base Ratio: A (33%), B (33%), C (33%), D (33%), E (35.1%), F (35.1%)

It means that you can get a item by over 100%(202.2%) ( A + B + C + D + E + F)

So Base Ratio is changed as follows for picking a item base on 100%.

Changed Base Ratio: A (16.32%), B (16.32%), C (16.32%), D (16.32%), E (17.35%), F (17.35%)

The total item drop chance is 202.2% so if you wanted to find the actual drop chance for "A" just put the numbers into the formula like this:

and thats how she got those numbers in the example above.

To figure out which mastery combination to use then follow this:

As a general rule of thumb to get the best chance of acquiring an item you want, just equip the specific mastery for the rarity of the item you want, and then use scavenger company mastery and treasure hunter if you need to get to 100% total item drop chance. So if you are looking for a green item, you want alibaba, blue or above you use Treasure island.

Treasure hunter and scavenger can't hurt but once you are past 100% total item drop chance they don't help either.