Mindflayers using netherese artifacts or a netherese mage using mindflayers
They have set up an interesting story.
If the artifact is indeed the contract between Gith and Tiamat and Shadowheart stole it then the followers of Shar must be desperate. Send a lvl 1 Cleric to steal the powerbase of the Gith? She was not alone, but she has it.
Sven promised an evil approach would be rewarding. As it is now it is mostly confusing. It feels like they changed the story at some point and only managed to implement half of the changes for early access.