Clearly what remains of The Mountain is under the sheet, still being experimented on since being severely wounded in his battle with the Red Viper. Qyburn is doing "whatever he can" as ordered by Cersei.

How could you overlook that the Office episode also teased guest spots by Jack Black, Jessica Alba, and Cloris Leachmen throughout the week and game only for it to all be in an offscreen TV movie about Jack Black falling in love with Cloris Leachmen.