Item Dupe
See the disambiguation page if you want information about duping in the other games.

The Item Dupe is a commonly used glitch in speedruns of Dark Souls. There are two types but both only replicate the effect of the item, they do not create another copy of it. Therefore, the term "dupe" is actually false but still the most logical name for it.
This glitch only works on patch versions newer than 1.05.

Procedure
This glitch abuses the following feature of the game:- Action Queuing: Performing an action (e.g. using an item, two-handing a weapon) during an animation causes this action to be queued up and executed only after the animation is over.

Type 1 - Items with confirmation box

The first type allows you to infinitely use items with a confirmation box, e.g. boss souls or Homeward Bones. However, it does not work with Red Eye Orbs since they are not being consumed at the time they are used.
To execute this, make sure you have the item you want to dupe highlighted in your hotbar first. Perform an action such as parrying, rolling or using a lever and queue up the use of the item by pressing PS3 Square.png | X360 Button x.png towards the end of the animation.
If you now press PS3 start.png | X360 Button start.png before the confirmation box appears, and use another item in your inventory (preferably Estus Flask or Darksign), the confirmation box of the item in your hotbar will still appear but actually confirming the use now does not consume the item in your hotbar. Instead it uses the item that you chose in your inventory but gives you the effect of the item with the confirmation box.
Also, make note of the variation in timings for different animations. For dupes off a parry you can hit the button almost immediately. Dupes off a lever pull or boss soul usage however require you to wait approximately until the last 10 frames of the animation before you are able to queue up an action.

Issues with female characters

Duping with this method doesn't work under all circumstances with a female character. One of the following prerequisites has to be met:

  • Two-handing any weapon or shield (allows normal duping, but obviously excludes the ability to dupe off a parry).
  • Having a weapon of one of the following weapon types equipped in the right hand: (Curved) Greatsword, Greataxe, Great Hammers, Spear, Halberd.

Type 2 - Items without confirmation box

The second type works on most items that have no confirmation box as well as on items with a confirmation box such as boss souls, but type 1 should be used for those. Notable here is that only the effect of very last one of the stack can be recreated. For example, if you carry 6 firebombs, you need to use up the first 5 before being able to duplicate the effects of the sixth one to throw a seventh, eighth, ... firebomb. It was discovered by Noobest in late 2013.
To execute this, as you use up your last item, queue up another use of it by pressing PS3 Square.png | X360 Button x.png again on the very last frames of the item-use animation where your item number still says "1".

Item Duping Window
Souls 1 Frame (= 33ms)
(Twin) Humanity 1 Frame (= 33ms)
(Black) Firebomb 2 Frames (= 66ms)

External Resources