Leviathan Blossom
From Super-wiki
History
A Leviathan Blossom is a special flower that grows exclusively in Purgatory. Combined with myrrh, cassia, and rockrose, it's nectar is one of the necessary ingredients for a spell designed to bind God, just as he and the archangels bound the Darkness.
Episodes
15.08 Our Father, Who Aren't in Heaven
After learning the truth about Chuck from Castiel, Michael gives him and Dean a spell with a list of ingredients that can bind God in his weakened state. One of which is the nectar of a Leviathan Blossom, which grows exclusively in Purgatory. To retrieve the flower, Michael opens a rift to Purgatory for Dean and Castiel that will last for 12 hours.