In D2R Ladder Items, runes are one pocketable item you can use to enhance your gear from the endgame with some other bonuses. But if you install runes in a particular order with a specific item, you receive a unique little bit of gear called a Runeword. Those items are some of the most effective gear from the game, but you are fiddly - if one makes a mistake slotting the runes to your gear, you need to destroy them to make it right.
New Runewords in many cases are added in patches, and Blizzard details the rune order needed to activate these new items. But from the Season 3 update, one Runeword within the patch notes showed a bad rune order, which typo has already established players wasting their runes in search of an item that's ultimately useless.
It seems the matter stems from some changes made within the PTR testing cycle. The Mosaic Runeword originally needed a Mal+Gul+Thul combo, but players weren't crazy about the cold damage supplied by Thul. So Mosaic became Mal+Gul+Amn, with Amn providing life steal instead.
Based on community discussion, it appears the patch notes were published initially while using the correct Mal+Gul+Amn combo, but sooner or later, a revision turned it time for Mal+Gul+Thul. They've now been corrected again, even so, the end result is there was of a day when Blizzard's mistake was happily encouraging players to waste their runes on the nonexistent Runeword.
It's not really a new buy d2 resurrected items: Resurrected season without some issues - remember when Season 2 was delayed because Blizzard "didn't plan very well"?