The new Runeword system in Diablo 4's Vessel of Hatred expansion is a lot of fun. These special stones slot into your armour and let you pinch skills from other classes, provided you generate enough of the Offering currency to fuel them. It seems a little complex at first, but the principle is actually very simple.
Runewords are made up of two runes, one which produces the Offering resource when you do a thing, while the second spends that resource to provide its effect. There are other certain intricacies, but that's about it. Here I'll run through how they work in a bit more depth below, the best ways to farm them, and at the bottom I'll include a full list of runes you can get.
Runes are a little like gems in that you can slot them onto your gear to provide secondary effects. There are two types of rune:
Some of these effects are class skills, while others are simply passives, but you need to slot both a Ritual Rune and an Invocation Rune together on a two-slotted piece of gear—such as legs, helmet, chest, or two-handed weapon—in order for them to work. If you provide more Offering than is needed to an Invocation Rune, it'll also gain an additional Overflow effect.
There are some other important details to remember about runes as well:
You can also use three runes of the same type to craft a new different rune, with a chance to create a rune of a higher rarity. Lastly, you can also craft Mythics—the new name for uber uniques—at the jeweller using runes.
Once you unlock Runewords in the Vessel of Hatred campaign, when you visit the council in the city of Kurast, you'll be able to get them through a variety of sources such as defeating bosses, whisper caches, strongholds, or as random drops from elites. The best way to get runes, however, is via the new Undercity activity. You can unlock this through the Kurast Undercity quest you can get from Ormus in the council chamber after you arrive there in the campaign.
You can also find Tributes in the Undercity and through other activities, which increase the rune rewards you get for completing the activity. Long story short; the Undercity is where you want to be if you need runes.
