I suspect that Item Discovery stacks.

[Burusagi]

So I was trying to farm the Dragoncrest+1 ring from the Desert Sorceresses. I equipped every single piece Item Discovery I had (Covetous Ring+1, Prisoner Hood/Tatters) and all I would find were pieces of their "armour".

I've been told that this is their rarest drop (because sexay).

So I figured I might've "overbuffed" my Item Discovery and removed everything but the Prisoner Hood an voilá - first kill got me the ring!

So I am guessing each mob has a different "tier" of drops, and the more Item Discover you have the more likely you are to get their "top drop".

[tcpl]

So I tossed a coin and got heads 5 times in a row. I then punched myself in the face, and my next coin toss got me tails! So I am guessing that punching oneself in the face influences coin tossing.

[Zefar]

Get the Traveling Merchant hat from the old lady in Majula. People have noticed that with that hat items seems to drop more often than with other item discovery hats.

[Saintilicious]

Yeah, you can stack item discovery up to a ridiculous amount with the right gear.

Set I've had the most success with:
Traveling Merchant Hat
Prisoner's Tatters
Covetous Gold Serpent Ring +2
Watchdragon Parma(Yes, it's a hidden attribute of the shield.)

And using a rusted coin afterwards(Lasts for 5 minutes.)

Edit: Almost got the full Desert Sorceress set in one run with that setup minus the coin.

[Zbegner000]

Just keep trying, its a super super rare drop. It took me ages to get it.

[Tirigon]

Originally posted by Zbegner000:

Just keep trying, its a super super rare drop. It took me ages to get it.:huntdeer:

Got about 10 of them while farming the "armor" set.

[Funpire]

I've farmed the set 5 times thus far. The only thing I noticed is with more discovery item gear, I get a wider range of drops and not specifically any more armor drops. I get the ring every farm session with no gear. That stupid ring... so many rings.

[Johnny The Fox]

Okay, equipment with an item discovery boost only affects the probability that enemies wil drop something. If they do, there is a separate set of probabilities that determines what the item will be, and what you wear has absolutely nothing to do with that. So, regardless of the item you're after, it always makes sense to wear all item discovery equipment you have. It's that simple, no need for "conspiracy theories". :D

[Burusagi]

Except that my idea is not a conspiracy theory - only "rare" drops when all decked out. Got the ring easily when I switched out.

[Johnny The Fox]

Well, I got two dragoncrest rings +1 and two full sets of their bellydancing outfit - errr, I mean their armor ;) - while farming the witches, without ever removing my jester's hat, prisoner's tatters or covetous gold serpent ring +2. I'm pretty sure the item discovery system works identically to that of Dark Souls I.