Remember when Scarrow first appeared and was bounty hunting that werewolf? Then we got to the city of Lavenham and Sian was doctorin' at the university? Sian was for the most part in control of their body, allowing Scarrow some free time to do whatever to release the pressure before taking the reigns again.
After being traumatized by Coven and Sansregret, Sian lost control and it went to Scarrow; it's been this way ever since...until Rapier banished out Scarrow's soul.
Sian, being confident he can take it from here, gets rid of Rapier in case Scarrow every got the idea to use the Soul Slap again. Unfortnately Deacon's orb summoning ritual is now in effect and Florina's piece is answering the call.
Things don't look great!