Animation World Network has an interesting piece discussing the truly international effort to creat VFX for Game of Thrones, with the work largely being handled and supervised by Pixomondo.
Episodes can range from having as few as 60 VFX shots to as many as 140 VFX shots (I’m guessing that upper end is where “Blackwater” falls). Some interesting notes about changes to the dragon design to show that they’re growing, and a lot of talk of how the work was handled by nine of the twelve Pixomondo studios across the globe, plus some work outsourced to other VFX production companies, Baked FX (which has a brief announcement about their involvement) and Entity FX.