I think the darkness is all part of a larger plan by Preta to take over everything. So we all know that Preta has been trying to take over the Woke people. She got rid of Moyra Salve in order to marry Utrim and become queen of the Woke. However, Utrim ran away (basically left her at the alter) which foiled her plans. Instead of being deterred, Preta came up w a new and better plan to take over everything. I think she used woke magic to create the darkness in order to distract the guardians. All she had to do was get Spyder to give it to Irixknee the Queen of the Fallen. Preta knew Irixknee would use darkness to start a war w guardians. I think Preta will come in at the last minute and cure the Darkness. Then she will be a hero. This will not only let her claim the Woke crown, but it will also make her the salvation of the guardians. Being that Zevdaya has already been bewitched by Heiress Moan, there really is no one to stand in Pretas way of also taking over the guardians. This will make the ruler of everything. Preta has been pulling the strings on everything since the beginning.