Remembrances in Elden Ring are items you can get from defeating powerful bosses, with one of the Dancing Lion being something you can use in the Shadow Of The Erdtree DLC. These vestiges of a Legend, Demigod, God, or other creature can be consumed for Runes or transformed. Boss weapons, Ashes of War, or strong Talismans can all be crafted from specific Remembrances your character collects.
https://screenrant.com/elden-ring-how-to-get-use-remembrance-dancing-lion/