Season 3 of introduces Nightmare Vaults, or larger dungeons you can unlock with special keys called Vault Sigils. These areas are filled with Construct enemies and bosses you can defeat for rare rewards. However, opening Vaults requires materials from world events exclusive to the seasonal content throughout Sanctuary.
Completing parts of the Season 3 questline will unlock four different Vaults you can delve into after defeating a boss lurking in one of them. Nightmare Vaults are harder versions of these dungeons and are only available in World Tier 3 in or higher. Scaling up the difficulty of your setting will lead to harder challenges but better rewards from these dangerous locations.
Vault Sigils are made from Pearls of Warding, which are special items you can find during Arcane Tremor seasonal world events. Similar to Helltides in or other events that show up on your Sanctuary map, Tremors appear randomly as you explore. You need to play through the story long enough to receive your Seneschal Companion before you can take part in these events as they happen.
Finishing an Arcane Tremor event will reward you with at least one Pearl of Warding you can take to an Occultist vendor. This NPC can transform the Pearls you collect into Vault Sigils or keys used to open one of the four upgraded Vaults found in Season 3 of. Earn enough Pearls to make at least a few Sigils since failure in a Vault requires another key for your character to return.
Vault Sigils are almost the exact same as Nightmare Sigils, which are used to open up Nightmare Dungeons in for a variety of loot, XP, and other rewards.
Spending Pearls of Warding in will also let you buy Zoltun's Warding, a blessing that increases your rewards from a Nightmare Vault. Using this divine gift right before entering a Vault maximizes your gifts from Wardwoven Chests, seen after the defeat of the dungeon's boss. Getting hurt by enemies or traps reduces the blessing you receive and diminishes your rewards by the time
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