|“||Accumulates experience as you complete Dungeons and Battle Arena matches. When fully charged it produces 5 Eclipse Shadow Keys. This effect can only trigger once a week.||”|
— Item Tooltip
The Eclipse Key Codex is a Tome gained at 270 Mastery. They produce 5 Eclipse Keys when they are fully charged. Unlike Common Tomes (that can be used as often as you like without cooldowns), these tomes can only be used once a week, although, they provide more rewards than Common Tomes per individual use.