Squash Flat (Combat)Source Inner Sea Gods pg. 216 (Amazon), Faiths of Corruption pg. 25 (Amazon)
You can bull rush an opponent straight to the ground.
Prerequisites: Improved Bull Rush, Merciless Rush, worshiper of Rovagug.
Benefit: Whenever you make a bull rush attack and your combat maneuver check exceeds the target’s CMD by 5 or more, you can attempt to trip the target as part of your bull rush as a free action. This does not provoke an attack of opportunity.Source Weapon Master's Handbook pg. 25 (Amazon)
After succeeding at a bull rush combat maneuver check, you can spend 4 stamina points to attempt to trip the target with Squash Flat regardless of your bull rush combat maneuver check’s result.