Why was this so long in coming?
Hail, Darkchild!!! Hail the Goblin Queen!!! My patience will be rewarded.
Lord Ewing *Praise His name! Uplift Him in song!* Your divine works will be remembered and glorified in worship for all eternity. Amen!
So is the little goblin Illya or Maddy or both?
It's happening!
It looks to me like the mystery villain is Belasco. I could have seen it being a new villain, but 'knowing' Illyana better than S'ym who has known her almost her whole life makes that seem very unlikely. There's also the parallel with the shadow monster from the children's story. Him having 2 arms is the only thing that gives me any pause, but Belasco has gone back on forth on having both arms or missing an arm. If it's not Belasco than the only only other thing I can see it being is the Darkchild. That's the only other villain who 'knows' Illyana that well, could be called 'master' by S'ym, and would know how to create a soul weapon for S'ym.