#3 Seth Rollins
Seth Rollins and Bray Wyatt have a well-documented rivalry dating back to their days as part of The Shield and The Wyatt Family respectively. The Architect is one of WWE's biggest faces right now and The Fiend could surely be a more than suitable opponent for him.
While this feud will help Rollins gain some lost momentum and new direction, The Fiend's terror will be creating a long-term impact on the minds of the people. It will also help in pushing Wyatt's character directly into the main event scene.
At present, Rollins is involved in a feud with Brock Lesnar and has not found any suitable opponent post-SummerSlam.
So, the option of this feud is wide open before the management. Thus, we may find The Fiend attacking Rollins at The Biggest Party Of The Summer itself.