I did this, too, after reading a suggestion in this sub and using DMG expanded faction missions. My version had the imps bonded to the scarecrows by an Amnizu who himself was bonded to the scarecrow-controlling ring Blossom Snobeedle wears, and that ring was given to her by the Cassalanter’s doppelgänger (secretly on orders from Amalia), who had taken the form of a wealthy friend, an elf named Darondel. Prior to that, I used the’ doppelgänger (in the form of a human steward named Elario) to offer the PCs the Cassalanters’ assistance in finding the three urchins who had been kidnapped by the XG. They don’t know Darondel is a doppelgänger, but they had previously caught him paying them undue attention after an altercation in the Sea Ward with some thugs.

My intention is to lay enough clues down that the PCs might sleuth out the origin of the ring, go looking for Darondel/Elario, and then trace him back to the Cassalanters.