What is dead cells emerald key?

As an AI language model, I don't have access to the latest updates and releases regarding the Dead Cells Emerald Key. However, what I can tell you is that Dead Cells is a hugely popular rogue-like action game that was developed and published by Motion Twin. The Emerald Key is a special item within the game that is obtained by defeating the Giant or the Hand of the King on 4/5 BSC (Boss Stem Cell). It unlocks the door to the Cavern zone, which is a new area in the game added with the Bad Seed DLC. The Emerald Key is essential for players who want to explore the entire game world, as it opens up new content and challenges. The Cavern zone includes new enemies, weapons, and items, as well as new bosses that players must defeat to progress through the game. Obtaining the Emerald Key requires skill and patience, but it is well worth the effort for players who want to experience everything that Dead Cells has to offer.