You’ll obtain Kanai’s Cube by starting a game on Adventure Mode and heading to town in any act. Once there, talk to the spirit of Zoltun Kulle, who will point you towards the Cube’s location and provide some history behind its creation and purpose.
Once you’ve obtained the Cube, you can use it by selecting it in town. Drag and drop items from your inventory into the Cube, then select the “Transmute” button to magically combine them.
Kanai’s Cube can be used to complete several Horadric rituals, which you can learn about through the Recipes menu. Next to the “Transmute” button, you’ll find a book icon—select it to view a list of available recipes for transmuting items. Several recipes will be available to you upon finding the Cube, and some of these require specific reagents found by completing bounties. Students of Horadric lore swear that the Cube allows for secret, undocumented item combinations to be transmuted.
Hope of Cain
Upgrades a level 70 item of Rare quality into a level 70 Legendary of the same item type. For example, upgrading a Rare one-handed sword will result in a random Legendary one-handed sword.
Skill of Nilfur
Transforms a Set item into another item belonging to the same Set. This recipe only works on Sets containing 3 or more pieces. For example,
Natalya's Embrace would be transformed into another random piece of the Natalya’s Vengeance set.
Darkness of Radament
Transforms 9 gems of one color into another. The resulting gem color varies depending on reagent used. You can buy gem reagents from Squirt the Peddler in Act 2.
Pleasure of Iben Fahd
Changes a stack of 100 crafting materials of one type into another. The resulting crafting material varies with the type of reagent used. For example, a stack of 100 Reusable Parts, when transmuted together with an item of Magic (Blue) quality, will result in a stack of 100 Arcane Dusts. A stack of 100 Arcane Dusts, when transmuted together with a Rare (Yellow) item, will result in a stack of 100 Veiled Crystals. Legendary crafting materials cannot be converted with this method.
Work of Cathan
Combine an item with a Rank 25 (or higher) Gem of Ease to lower the character level required to use that item to 1.
Law of Kulle
Sacrificing great quantities of magical ingredients, the Horadric incantation known as the Law of Kulle allows you to reforge any Legendary or Set item. This process will grant your item different attributes, and may transform it into an Ancient or Primal Ancient version of the same item.
Be warned; reforging an Ancient or Primal Ancient Legendary or Set item might result in the loss of the Ancient or Primal Ancient property.
Caldesann’s Despair
Enchants an Ancient or Primal Ancient Legendary or Set item with additional attribute points. The resulting attribute depends on the gem color used. Using this recipe with 3 Flawless Royal Rubies will augment an item with Strength, 3 Flawless Royal Topazes will add Intelligence, 3 Flawless Royal Emeralds will add Dexterity, and 3 Flawless Royal Amethysts will add Vitality. To augment an Ancient or Primal Ancient weapon, a Legendary Gem of Rank 30 or higher is required. Augmenting an Ancient or Primal Ancient Ring or Amulet requires a Legendary Gem of Rank 40 or higher, while augmenting an Ancient or Primal Ancient piece of armor requires a Legendary Gem of Rank 50 or higher. The higher the rank of the Legendary Gem used, the more attribute points will be added to your item.
With Kanai's Cube, you can destroy a Legendary item and store its power. Most Legendary powers can be extracted—these are highlighted in orange when you hover over a Legendary item to view its attributes.
You may use up to three extracted Legendary powers at once; one from a weapon slot (main-hand, off-hand), one from an armor slot (chest, waist, legs, feet, hands, arms), and one from a jewelry slot (ring, amulet).